Pathology in Complex Analysis

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Complex analysis is the good twin and real analysis the evil one:
beautiful formulas and elegant theorems seem to blossom spontaneously
in the complex domain, while toil and pathology rule the reals. ~
Charles Pugh




People often like to talk about elegant "miracles" in Complex Analysis. However, what's are "pathological" objects/properties in Complex Analysis?



EDIT (09/13/18): Also posted as
https://math.stackexchange.com/questions/2912320/most-pathological-object-in-complex-analysis



EDIT: Changed the wording of the question.










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  • 3




    First, this does not seem to be on-topic here, since it is not of research level; better ask it on MSE, where you do have an account. Second, who is Charles Pugh, given that Google only finds 8 results about this name, 4 of which from the 18th and 19th centuries?
    – Alex M.
    21 hours ago






  • 3




    Charles Chapman Pugh
    – Robert Israel
    21 hours ago






  • 15




    @AlexM. To be honest, I have read far more well-received big-list questions on MO than on MSE. Questions like these can be found in great number in the all time highest votes lists. I do not qualify as someone who can judge whether this is on-topic, but I wonder whether we have double standards, or whether the acceptability of questions has changed over time.
    – M. Winter
    20 hours ago






  • 4




    This question is perfectly fine for MO, and why does it matter who Charles Pugh is? If his quote is a good way to frame the question, then why not use it?
    – arsmath
    20 hours ago






  • 4




    @j.c. I think the point of the question is for OP to not specify that and leave it open to interpretation.
    – Zachary Selk
    19 hours ago














up vote
19
down vote

favorite
6













Complex analysis is the good twin and real analysis the evil one:
beautiful formulas and elegant theorems seem to blossom spontaneously
in the complex domain, while toil and pathology rule the reals. ~
Charles Pugh




People often like to talk about elegant "miracles" in Complex Analysis. However, what's are "pathological" objects/properties in Complex Analysis?



EDIT (09/13/18): Also posted as
https://math.stackexchange.com/questions/2912320/most-pathological-object-in-complex-analysis



EDIT: Changed the wording of the question.










share|cite|improve this question



















  • 3




    First, this does not seem to be on-topic here, since it is not of research level; better ask it on MSE, where you do have an account. Second, who is Charles Pugh, given that Google only finds 8 results about this name, 4 of which from the 18th and 19th centuries?
    – Alex M.
    21 hours ago






  • 3




    Charles Chapman Pugh
    – Robert Israel
    21 hours ago






  • 15




    @AlexM. To be honest, I have read far more well-received big-list questions on MO than on MSE. Questions like these can be found in great number in the all time highest votes lists. I do not qualify as someone who can judge whether this is on-topic, but I wonder whether we have double standards, or whether the acceptability of questions has changed over time.
    – M. Winter
    20 hours ago






  • 4




    This question is perfectly fine for MO, and why does it matter who Charles Pugh is? If his quote is a good way to frame the question, then why not use it?
    – arsmath
    20 hours ago






  • 4




    @j.c. I think the point of the question is for OP to not specify that and leave it open to interpretation.
    – Zachary Selk
    19 hours ago












up vote
19
down vote

favorite
6









up vote
19
down vote

favorite
6






6






Complex analysis is the good twin and real analysis the evil one:
beautiful formulas and elegant theorems seem to blossom spontaneously
in the complex domain, while toil and pathology rule the reals. ~
Charles Pugh




People often like to talk about elegant "miracles" in Complex Analysis. However, what's are "pathological" objects/properties in Complex Analysis?



EDIT (09/13/18): Also posted as
https://math.stackexchange.com/questions/2912320/most-pathological-object-in-complex-analysis



EDIT: Changed the wording of the question.










share|cite|improve this question
















Complex analysis is the good twin and real analysis the evil one:
beautiful formulas and elegant theorems seem to blossom spontaneously
in the complex domain, while toil and pathology rule the reals. ~
Charles Pugh




People often like to talk about elegant "miracles" in Complex Analysis. However, what's are "pathological" objects/properties in Complex Analysis?



EDIT (09/13/18): Also posted as
https://math.stackexchange.com/questions/2912320/most-pathological-object-in-complex-analysis



EDIT: Changed the wording of the question.







cv.complex-variables






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edited 5 hours ago


























community wiki





3 revs, 2 users 81%
Qi Zhu








  • 3




    First, this does not seem to be on-topic here, since it is not of research level; better ask it on MSE, where you do have an account. Second, who is Charles Pugh, given that Google only finds 8 results about this name, 4 of which from the 18th and 19th centuries?
    – Alex M.
    21 hours ago






  • 3




    Charles Chapman Pugh
    – Robert Israel
    21 hours ago






  • 15




    @AlexM. To be honest, I have read far more well-received big-list questions on MO than on MSE. Questions like these can be found in great number in the all time highest votes lists. I do not qualify as someone who can judge whether this is on-topic, but I wonder whether we have double standards, or whether the acceptability of questions has changed over time.
    – M. Winter
    20 hours ago






  • 4




    This question is perfectly fine for MO, and why does it matter who Charles Pugh is? If his quote is a good way to frame the question, then why not use it?
    – arsmath
    20 hours ago






  • 4




    @j.c. I think the point of the question is for OP to not specify that and leave it open to interpretation.
    – Zachary Selk
    19 hours ago












  • 3




    First, this does not seem to be on-topic here, since it is not of research level; better ask it on MSE, where you do have an account. Second, who is Charles Pugh, given that Google only finds 8 results about this name, 4 of which from the 18th and 19th centuries?
    – Alex M.
    21 hours ago






  • 3




    Charles Chapman Pugh
    – Robert Israel
    21 hours ago






  • 15




    @AlexM. To be honest, I have read far more well-received big-list questions on MO than on MSE. Questions like these can be found in great number in the all time highest votes lists. I do not qualify as someone who can judge whether this is on-topic, but I wonder whether we have double standards, or whether the acceptability of questions has changed over time.
    – M. Winter
    20 hours ago






  • 4




    This question is perfectly fine for MO, and why does it matter who Charles Pugh is? If his quote is a good way to frame the question, then why not use it?
    – arsmath
    20 hours ago






  • 4




    @j.c. I think the point of the question is for OP to not specify that and leave it open to interpretation.
    – Zachary Selk
    19 hours ago







3




3




First, this does not seem to be on-topic here, since it is not of research level; better ask it on MSE, where you do have an account. Second, who is Charles Pugh, given that Google only finds 8 results about this name, 4 of which from the 18th and 19th centuries?
– Alex M.
21 hours ago




First, this does not seem to be on-topic here, since it is not of research level; better ask it on MSE, where you do have an account. Second, who is Charles Pugh, given that Google only finds 8 results about this name, 4 of which from the 18th and 19th centuries?
– Alex M.
21 hours ago




3




3




Charles Chapman Pugh
– Robert Israel
21 hours ago




Charles Chapman Pugh
– Robert Israel
21 hours ago




15




15




@AlexM. To be honest, I have read far more well-received big-list questions on MO than on MSE. Questions like these can be found in great number in the all time highest votes lists. I do not qualify as someone who can judge whether this is on-topic, but I wonder whether we have double standards, or whether the acceptability of questions has changed over time.
– M. Winter
20 hours ago




@AlexM. To be honest, I have read far more well-received big-list questions on MO than on MSE. Questions like these can be found in great number in the all time highest votes lists. I do not qualify as someone who can judge whether this is on-topic, but I wonder whether we have double standards, or whether the acceptability of questions has changed over time.
– M. Winter
20 hours ago




4




4




This question is perfectly fine for MO, and why does it matter who Charles Pugh is? If his quote is a good way to frame the question, then why not use it?
– arsmath
20 hours ago




This question is perfectly fine for MO, and why does it matter who Charles Pugh is? If his quote is a good way to frame the question, then why not use it?
– arsmath
20 hours ago




4




4




@j.c. I think the point of the question is for OP to not specify that and leave it open to interpretation.
– Zachary Selk
19 hours ago




@j.c. I think the point of the question is for OP to not specify that and leave it open to interpretation.
– Zachary Selk
19 hours ago










6 Answers
6






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up vote
21
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I would say that Mandelbrot set (like similar fractal objects coming from complex dynamics) can be seen as a "pathological" object, at least from the point of view of regularity (the boundary is nowhere differentiable, for instance).






share|cite|improve this answer





























    up vote
    17
    down vote













    I don't know how you want to define "pathological", but some of the corollaries of Runge's theorem give you functions with interesting properties. One of mine: there is a rational function $f$ such that for every holomorphic function $g$ on the open unit disk $mathbb D$, $g$ or $g-f$ has a zero in $mathbb D$.
    This is American Mathematical Monthly problem 6520, solution at www.jstor.org/stable/2323638






    share|cite|improve this answer





























      up vote
      11
      down vote













      In an old MO question of mine, I had wondered the following (I'm quoting my question):




      Let D ⊂ ℂ be the closed unit disc in the complex plane, and let C be a continuously embedded path in D between the points -1 and 1. The curve C splits D into two halves $D_1$ and $D_2$.



      Let f : D→ℂ be a continuous function that is holomorphic on the interiors of $D_1$ and $D_2$.
      Is f then necessarily holomorphic?




      The answer turns out to be no.






      share|cite|improve this answer





























        up vote
        10
        down vote













        A natural boundary is probably rather pathological, in the same spirit as that continuous-everywhere-but-differentiable-nowhere and smooth-everywhere-but-analytic-nowhere functions are in real analysis. In particular, it consists of a function which has a property (analytic) that one might intuitively expect would lead to another (analytic continuation, to at least some extent), but doesn't.



        A simple example is the series function:



        $$f(z) = sum_n=0^infty z^2^n$$



        This function is defined on $|z| < 1$, but the circle $|z| = 1$ is singular, and the series thus both converges on the maximal domain and forbids any extension beyond it. The latter curve is thus a natural boundary - an enclosing wall singularity that prevents any further extension of the function's domain to an area of nontrivial measure.






        share|cite|improve this answer


















        • 1




          In this case, I had to revise my intuition several times. At first analytic continuation was counter-intuitive because I expected analytic functions to behave like continuous ones (having partitions of unity). After that, natural boundaries were counter-intuitive because I expected analytic continuation to always be possible. Then when I found out about domains of holomorphy in several complex variables, that was counter-intuitive because you do get some analytic continuation for free as long as the complex dimension $> 1$.
          – Robert Furber
          2 hours ago

















        up vote
        6
        down vote













        The rigidity of complex domains in higher dimension For example the unit ball in $mathbbC^2$ is not holomorphic equivalent to the unit cube.






        share|cite|improve this answer





























          up vote
          4
          down vote













          I'd say that multivariable complex analysis is more complicated relative to single variable complex analysis than multivariable real analysis is to single variable real analysis. There are new phenomena that could charitably be called 'rich' and uncharitably be called 'pathological.'



          For instance, it's well known that there are no non-constant holomorphic functions on 1D compact complex manifolds, but there are always non-constant meromorphic functions. In higher dimensions there are compact complex manifolds without even any non-constant meromorphic functions.



          Another thing is related to The_Sympathizer's answer: Any open set in $mathbbC$ can be the 'domain of holomorphicity' of a holomorphic function, i.e. a domain which beyond which the function cannot be analytically extended. In higher dimensions this is no longer true and characterizing the open sets which are domains of holomorphicity becomes somewhat complicated.






          share|cite|improve this answer






















          • Complex tori that aren't abelian varieties are examples of the pathology in your second paragraph, right?
            – Robert Furber
            2 hours ago










          • Yeah, those are the example I know of.
            – James Hanson
            4 mins ago










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          6 Answers
          6






          active

          oldest

          votes








          6 Answers
          6






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes








          up vote
          21
          down vote













          I would say that Mandelbrot set (like similar fractal objects coming from complex dynamics) can be seen as a "pathological" object, at least from the point of view of regularity (the boundary is nowhere differentiable, for instance).






          share|cite|improve this answer


























            up vote
            21
            down vote













            I would say that Mandelbrot set (like similar fractal objects coming from complex dynamics) can be seen as a "pathological" object, at least from the point of view of regularity (the boundary is nowhere differentiable, for instance).






            share|cite|improve this answer
























              up vote
              21
              down vote










              up vote
              21
              down vote









              I would say that Mandelbrot set (like similar fractal objects coming from complex dynamics) can be seen as a "pathological" object, at least from the point of view of regularity (the boundary is nowhere differentiable, for instance).






              share|cite|improve this answer














              I would say that Mandelbrot set (like similar fractal objects coming from complex dynamics) can be seen as a "pathological" object, at least from the point of view of regularity (the boundary is nowhere differentiable, for instance).







              share|cite|improve this answer














              share|cite|improve this answer



              share|cite|improve this answer








              answered 20 hours ago


























              community wiki





              Francesco Polizzi





















                  up vote
                  17
                  down vote













                  I don't know how you want to define "pathological", but some of the corollaries of Runge's theorem give you functions with interesting properties. One of mine: there is a rational function $f$ such that for every holomorphic function $g$ on the open unit disk $mathbb D$, $g$ or $g-f$ has a zero in $mathbb D$.
                  This is American Mathematical Monthly problem 6520, solution at www.jstor.org/stable/2323638






                  share|cite|improve this answer


























                    up vote
                    17
                    down vote













                    I don't know how you want to define "pathological", but some of the corollaries of Runge's theorem give you functions with interesting properties. One of mine: there is a rational function $f$ such that for every holomorphic function $g$ on the open unit disk $mathbb D$, $g$ or $g-f$ has a zero in $mathbb D$.
                    This is American Mathematical Monthly problem 6520, solution at www.jstor.org/stable/2323638






                    share|cite|improve this answer
























                      up vote
                      17
                      down vote










                      up vote
                      17
                      down vote









                      I don't know how you want to define "pathological", but some of the corollaries of Runge's theorem give you functions with interesting properties. One of mine: there is a rational function $f$ such that for every holomorphic function $g$ on the open unit disk $mathbb D$, $g$ or $g-f$ has a zero in $mathbb D$.
                      This is American Mathematical Monthly problem 6520, solution at www.jstor.org/stable/2323638






                      share|cite|improve this answer














                      I don't know how you want to define "pathological", but some of the corollaries of Runge's theorem give you functions with interesting properties. One of mine: there is a rational function $f$ such that for every holomorphic function $g$ on the open unit disk $mathbb D$, $g$ or $g-f$ has a zero in $mathbb D$.
                      This is American Mathematical Monthly problem 6520, solution at www.jstor.org/stable/2323638







                      share|cite|improve this answer














                      share|cite|improve this answer



                      share|cite|improve this answer








                      answered 21 hours ago


























                      community wiki





                      Robert Israel





















                          up vote
                          11
                          down vote













                          In an old MO question of mine, I had wondered the following (I'm quoting my question):




                          Let D ⊂ ℂ be the closed unit disc in the complex plane, and let C be a continuously embedded path in D between the points -1 and 1. The curve C splits D into two halves $D_1$ and $D_2$.



                          Let f : D→ℂ be a continuous function that is holomorphic on the interiors of $D_1$ and $D_2$.
                          Is f then necessarily holomorphic?




                          The answer turns out to be no.






                          share|cite|improve this answer


























                            up vote
                            11
                            down vote













                            In an old MO question of mine, I had wondered the following (I'm quoting my question):




                            Let D ⊂ ℂ be the closed unit disc in the complex plane, and let C be a continuously embedded path in D between the points -1 and 1. The curve C splits D into two halves $D_1$ and $D_2$.



                            Let f : D→ℂ be a continuous function that is holomorphic on the interiors of $D_1$ and $D_2$.
                            Is f then necessarily holomorphic?




                            The answer turns out to be no.






                            share|cite|improve this answer
























                              up vote
                              11
                              down vote










                              up vote
                              11
                              down vote









                              In an old MO question of mine, I had wondered the following (I'm quoting my question):




                              Let D ⊂ ℂ be the closed unit disc in the complex plane, and let C be a continuously embedded path in D between the points -1 and 1. The curve C splits D into two halves $D_1$ and $D_2$.



                              Let f : D→ℂ be a continuous function that is holomorphic on the interiors of $D_1$ and $D_2$.
                              Is f then necessarily holomorphic?




                              The answer turns out to be no.






                              share|cite|improve this answer














                              In an old MO question of mine, I had wondered the following (I'm quoting my question):




                              Let D ⊂ ℂ be the closed unit disc in the complex plane, and let C be a continuously embedded path in D between the points -1 and 1. The curve C splits D into two halves $D_1$ and $D_2$.



                              Let f : D→ℂ be a continuous function that is holomorphic on the interiors of $D_1$ and $D_2$.
                              Is f then necessarily holomorphic?




                              The answer turns out to be no.







                              share|cite|improve this answer














                              share|cite|improve this answer



                              share|cite|improve this answer








                              edited 11 hours ago


























                              community wiki





                              André Henriques





















                                  up vote
                                  10
                                  down vote













                                  A natural boundary is probably rather pathological, in the same spirit as that continuous-everywhere-but-differentiable-nowhere and smooth-everywhere-but-analytic-nowhere functions are in real analysis. In particular, it consists of a function which has a property (analytic) that one might intuitively expect would lead to another (analytic continuation, to at least some extent), but doesn't.



                                  A simple example is the series function:



                                  $$f(z) = sum_n=0^infty z^2^n$$



                                  This function is defined on $|z| < 1$, but the circle $|z| = 1$ is singular, and the series thus both converges on the maximal domain and forbids any extension beyond it. The latter curve is thus a natural boundary - an enclosing wall singularity that prevents any further extension of the function's domain to an area of nontrivial measure.






                                  share|cite|improve this answer


















                                  • 1




                                    In this case, I had to revise my intuition several times. At first analytic continuation was counter-intuitive because I expected analytic functions to behave like continuous ones (having partitions of unity). After that, natural boundaries were counter-intuitive because I expected analytic continuation to always be possible. Then when I found out about domains of holomorphy in several complex variables, that was counter-intuitive because you do get some analytic continuation for free as long as the complex dimension $> 1$.
                                    – Robert Furber
                                    2 hours ago














                                  up vote
                                  10
                                  down vote













                                  A natural boundary is probably rather pathological, in the same spirit as that continuous-everywhere-but-differentiable-nowhere and smooth-everywhere-but-analytic-nowhere functions are in real analysis. In particular, it consists of a function which has a property (analytic) that one might intuitively expect would lead to another (analytic continuation, to at least some extent), but doesn't.



                                  A simple example is the series function:



                                  $$f(z) = sum_n=0^infty z^2^n$$



                                  This function is defined on $|z| < 1$, but the circle $|z| = 1$ is singular, and the series thus both converges on the maximal domain and forbids any extension beyond it. The latter curve is thus a natural boundary - an enclosing wall singularity that prevents any further extension of the function's domain to an area of nontrivial measure.






                                  share|cite|improve this answer


















                                  • 1




                                    In this case, I had to revise my intuition several times. At first analytic continuation was counter-intuitive because I expected analytic functions to behave like continuous ones (having partitions of unity). After that, natural boundaries were counter-intuitive because I expected analytic continuation to always be possible. Then when I found out about domains of holomorphy in several complex variables, that was counter-intuitive because you do get some analytic continuation for free as long as the complex dimension $> 1$.
                                    – Robert Furber
                                    2 hours ago












                                  up vote
                                  10
                                  down vote










                                  up vote
                                  10
                                  down vote









                                  A natural boundary is probably rather pathological, in the same spirit as that continuous-everywhere-but-differentiable-nowhere and smooth-everywhere-but-analytic-nowhere functions are in real analysis. In particular, it consists of a function which has a property (analytic) that one might intuitively expect would lead to another (analytic continuation, to at least some extent), but doesn't.



                                  A simple example is the series function:



                                  $$f(z) = sum_n=0^infty z^2^n$$



                                  This function is defined on $|z| < 1$, but the circle $|z| = 1$ is singular, and the series thus both converges on the maximal domain and forbids any extension beyond it. The latter curve is thus a natural boundary - an enclosing wall singularity that prevents any further extension of the function's domain to an area of nontrivial measure.






                                  share|cite|improve this answer














                                  A natural boundary is probably rather pathological, in the same spirit as that continuous-everywhere-but-differentiable-nowhere and smooth-everywhere-but-analytic-nowhere functions are in real analysis. In particular, it consists of a function which has a property (analytic) that one might intuitively expect would lead to another (analytic continuation, to at least some extent), but doesn't.



                                  A simple example is the series function:



                                  $$f(z) = sum_n=0^infty z^2^n$$



                                  This function is defined on $|z| < 1$, but the circle $|z| = 1$ is singular, and the series thus both converges on the maximal domain and forbids any extension beyond it. The latter curve is thus a natural boundary - an enclosing wall singularity that prevents any further extension of the function's domain to an area of nontrivial measure.







                                  share|cite|improve this answer














                                  share|cite|improve this answer



                                  share|cite|improve this answer








                                  answered 11 hours ago


























                                  community wiki





                                  The_Sympathizer








                                  • 1




                                    In this case, I had to revise my intuition several times. At first analytic continuation was counter-intuitive because I expected analytic functions to behave like continuous ones (having partitions of unity). After that, natural boundaries were counter-intuitive because I expected analytic continuation to always be possible. Then when I found out about domains of holomorphy in several complex variables, that was counter-intuitive because you do get some analytic continuation for free as long as the complex dimension $> 1$.
                                    – Robert Furber
                                    2 hours ago












                                  • 1




                                    In this case, I had to revise my intuition several times. At first analytic continuation was counter-intuitive because I expected analytic functions to behave like continuous ones (having partitions of unity). After that, natural boundaries were counter-intuitive because I expected analytic continuation to always be possible. Then when I found out about domains of holomorphy in several complex variables, that was counter-intuitive because you do get some analytic continuation for free as long as the complex dimension $> 1$.
                                    – Robert Furber
                                    2 hours ago







                                  1




                                  1




                                  In this case, I had to revise my intuition several times. At first analytic continuation was counter-intuitive because I expected analytic functions to behave like continuous ones (having partitions of unity). After that, natural boundaries were counter-intuitive because I expected analytic continuation to always be possible. Then when I found out about domains of holomorphy in several complex variables, that was counter-intuitive because you do get some analytic continuation for free as long as the complex dimension $> 1$.
                                  – Robert Furber
                                  2 hours ago




                                  In this case, I had to revise my intuition several times. At first analytic continuation was counter-intuitive because I expected analytic functions to behave like continuous ones (having partitions of unity). After that, natural boundaries were counter-intuitive because I expected analytic continuation to always be possible. Then when I found out about domains of holomorphy in several complex variables, that was counter-intuitive because you do get some analytic continuation for free as long as the complex dimension $> 1$.
                                  – Robert Furber
                                  2 hours ago










                                  up vote
                                  6
                                  down vote













                                  The rigidity of complex domains in higher dimension For example the unit ball in $mathbbC^2$ is not holomorphic equivalent to the unit cube.






                                  share|cite|improve this answer


























                                    up vote
                                    6
                                    down vote













                                    The rigidity of complex domains in higher dimension For example the unit ball in $mathbbC^2$ is not holomorphic equivalent to the unit cube.






                                    share|cite|improve this answer
























                                      up vote
                                      6
                                      down vote










                                      up vote
                                      6
                                      down vote









                                      The rigidity of complex domains in higher dimension For example the unit ball in $mathbbC^2$ is not holomorphic equivalent to the unit cube.






                                      share|cite|improve this answer














                                      The rigidity of complex domains in higher dimension For example the unit ball in $mathbbC^2$ is not holomorphic equivalent to the unit cube.







                                      share|cite|improve this answer














                                      share|cite|improve this answer



                                      share|cite|improve this answer








                                      answered 6 hours ago


























                                      community wiki





                                      Ali Taghavi





















                                          up vote
                                          4
                                          down vote













                                          I'd say that multivariable complex analysis is more complicated relative to single variable complex analysis than multivariable real analysis is to single variable real analysis. There are new phenomena that could charitably be called 'rich' and uncharitably be called 'pathological.'



                                          For instance, it's well known that there are no non-constant holomorphic functions on 1D compact complex manifolds, but there are always non-constant meromorphic functions. In higher dimensions there are compact complex manifolds without even any non-constant meromorphic functions.



                                          Another thing is related to The_Sympathizer's answer: Any open set in $mathbbC$ can be the 'domain of holomorphicity' of a holomorphic function, i.e. a domain which beyond which the function cannot be analytically extended. In higher dimensions this is no longer true and characterizing the open sets which are domains of holomorphicity becomes somewhat complicated.






                                          share|cite|improve this answer






















                                          • Complex tori that aren't abelian varieties are examples of the pathology in your second paragraph, right?
                                            – Robert Furber
                                            2 hours ago










                                          • Yeah, those are the example I know of.
                                            – James Hanson
                                            4 mins ago














                                          up vote
                                          4
                                          down vote













                                          I'd say that multivariable complex analysis is more complicated relative to single variable complex analysis than multivariable real analysis is to single variable real analysis. There are new phenomena that could charitably be called 'rich' and uncharitably be called 'pathological.'



                                          For instance, it's well known that there are no non-constant holomorphic functions on 1D compact complex manifolds, but there are always non-constant meromorphic functions. In higher dimensions there are compact complex manifolds without even any non-constant meromorphic functions.



                                          Another thing is related to The_Sympathizer's answer: Any open set in $mathbbC$ can be the 'domain of holomorphicity' of a holomorphic function, i.e. a domain which beyond which the function cannot be analytically extended. In higher dimensions this is no longer true and characterizing the open sets which are domains of holomorphicity becomes somewhat complicated.






                                          share|cite|improve this answer






















                                          • Complex tori that aren't abelian varieties are examples of the pathology in your second paragraph, right?
                                            – Robert Furber
                                            2 hours ago










                                          • Yeah, those are the example I know of.
                                            – James Hanson
                                            4 mins ago












                                          up vote
                                          4
                                          down vote










                                          up vote
                                          4
                                          down vote









                                          I'd say that multivariable complex analysis is more complicated relative to single variable complex analysis than multivariable real analysis is to single variable real analysis. There are new phenomena that could charitably be called 'rich' and uncharitably be called 'pathological.'



                                          For instance, it's well known that there are no non-constant holomorphic functions on 1D compact complex manifolds, but there are always non-constant meromorphic functions. In higher dimensions there are compact complex manifolds without even any non-constant meromorphic functions.



                                          Another thing is related to The_Sympathizer's answer: Any open set in $mathbbC$ can be the 'domain of holomorphicity' of a holomorphic function, i.e. a domain which beyond which the function cannot be analytically extended. In higher dimensions this is no longer true and characterizing the open sets which are domains of holomorphicity becomes somewhat complicated.






                                          share|cite|improve this answer














                                          I'd say that multivariable complex analysis is more complicated relative to single variable complex analysis than multivariable real analysis is to single variable real analysis. There are new phenomena that could charitably be called 'rich' and uncharitably be called 'pathological.'



                                          For instance, it's well known that there are no non-constant holomorphic functions on 1D compact complex manifolds, but there are always non-constant meromorphic functions. In higher dimensions there are compact complex manifolds without even any non-constant meromorphic functions.



                                          Another thing is related to The_Sympathizer's answer: Any open set in $mathbbC$ can be the 'domain of holomorphicity' of a holomorphic function, i.e. a domain which beyond which the function cannot be analytically extended. In higher dimensions this is no longer true and characterizing the open sets which are domains of holomorphicity becomes somewhat complicated.







                                          share|cite|improve this answer














                                          share|cite|improve this answer



                                          share|cite|improve this answer








                                          answered 7 hours ago


























                                          community wiki





                                          James Hanson












                                          • Complex tori that aren't abelian varieties are examples of the pathology in your second paragraph, right?
                                            – Robert Furber
                                            2 hours ago










                                          • Yeah, those are the example I know of.
                                            – James Hanson
                                            4 mins ago
















                                          • Complex tori that aren't abelian varieties are examples of the pathology in your second paragraph, right?
                                            – Robert Furber
                                            2 hours ago










                                          • Yeah, those are the example I know of.
                                            – James Hanson
                                            4 mins ago















                                          Complex tori that aren't abelian varieties are examples of the pathology in your second paragraph, right?
                                          – Robert Furber
                                          2 hours ago




                                          Complex tori that aren't abelian varieties are examples of the pathology in your second paragraph, right?
                                          – Robert Furber
                                          2 hours ago












                                          Yeah, those are the example I know of.
                                          – James Hanson
                                          4 mins ago




                                          Yeah, those are the example I know of.
                                          – James Hanson
                                          4 mins ago

















                                           

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