Decomposing functions to Taylor-Fourier series












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A great many functions can be expressed as a series of the form



$$ U_0(x) + U_1(x) x + U_2(x) frac{1}{2!}x(x-1) + ... $$



Where $U_r(x)$ are integrable periodic functions with period $1$. Call such functions "1 periodic normal" functions. Note that the $U_r(x)$ being periodic can be decomposed into their fourier series as:



$$ U_r(x) = sum_{k=-infty}^{infty} a_{r,k} e^{2pi i k x} $$



And so 1-periodic normal functions have a general form as:



$$ sum_{k=-infty}^{infty} a_{0,k} e^{2pi i k x} + left( sum_{k=-infty}^{infty} a_{1,k} e^{2pi i k x} right) x + ... $$



In the event that $U_1, U_2 ... $ are equal to $0$ it follows that we can use fourier analysis to determine the coefficients of $U_0$.



In particular when $U_1, U_2 ... $ are equal to 0, then the operator



$$ f rightarrow 2 int_{0}^{1}f(x) e^{ipi Jx} dx $$



Gives the coefficient $a_{j,0}$ of our series.



Suppose we have no guarantees about non-zero $U_r$ how could we systematically determine the $a_{j,r}$ coefficients of our series?










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    1












    $begingroup$


    A great many functions can be expressed as a series of the form



    $$ U_0(x) + U_1(x) x + U_2(x) frac{1}{2!}x(x-1) + ... $$



    Where $U_r(x)$ are integrable periodic functions with period $1$. Call such functions "1 periodic normal" functions. Note that the $U_r(x)$ being periodic can be decomposed into their fourier series as:



    $$ U_r(x) = sum_{k=-infty}^{infty} a_{r,k} e^{2pi i k x} $$



    And so 1-periodic normal functions have a general form as:



    $$ sum_{k=-infty}^{infty} a_{0,k} e^{2pi i k x} + left( sum_{k=-infty}^{infty} a_{1,k} e^{2pi i k x} right) x + ... $$



    In the event that $U_1, U_2 ... $ are equal to $0$ it follows that we can use fourier analysis to determine the coefficients of $U_0$.



    In particular when $U_1, U_2 ... $ are equal to 0, then the operator



    $$ f rightarrow 2 int_{0}^{1}f(x) e^{ipi Jx} dx $$



    Gives the coefficient $a_{j,0}$ of our series.



    Suppose we have no guarantees about non-zero $U_r$ how could we systematically determine the $a_{j,r}$ coefficients of our series?










    share|cite|improve this question











    $endgroup$















      1












      1








      1





      $begingroup$


      A great many functions can be expressed as a series of the form



      $$ U_0(x) + U_1(x) x + U_2(x) frac{1}{2!}x(x-1) + ... $$



      Where $U_r(x)$ are integrable periodic functions with period $1$. Call such functions "1 periodic normal" functions. Note that the $U_r(x)$ being periodic can be decomposed into their fourier series as:



      $$ U_r(x) = sum_{k=-infty}^{infty} a_{r,k} e^{2pi i k x} $$



      And so 1-periodic normal functions have a general form as:



      $$ sum_{k=-infty}^{infty} a_{0,k} e^{2pi i k x} + left( sum_{k=-infty}^{infty} a_{1,k} e^{2pi i k x} right) x + ... $$



      In the event that $U_1, U_2 ... $ are equal to $0$ it follows that we can use fourier analysis to determine the coefficients of $U_0$.



      In particular when $U_1, U_2 ... $ are equal to 0, then the operator



      $$ f rightarrow 2 int_{0}^{1}f(x) e^{ipi Jx} dx $$



      Gives the coefficient $a_{j,0}$ of our series.



      Suppose we have no guarantees about non-zero $U_r$ how could we systematically determine the $a_{j,r}$ coefficients of our series?










      share|cite|improve this question











      $endgroup$




      A great many functions can be expressed as a series of the form



      $$ U_0(x) + U_1(x) x + U_2(x) frac{1}{2!}x(x-1) + ... $$



      Where $U_r(x)$ are integrable periodic functions with period $1$. Call such functions "1 periodic normal" functions. Note that the $U_r(x)$ being periodic can be decomposed into their fourier series as:



      $$ U_r(x) = sum_{k=-infty}^{infty} a_{r,k} e^{2pi i k x} $$



      And so 1-periodic normal functions have a general form as:



      $$ sum_{k=-infty}^{infty} a_{0,k} e^{2pi i k x} + left( sum_{k=-infty}^{infty} a_{1,k} e^{2pi i k x} right) x + ... $$



      In the event that $U_1, U_2 ... $ are equal to $0$ it follows that we can use fourier analysis to determine the coefficients of $U_0$.



      In particular when $U_1, U_2 ... $ are equal to 0, then the operator



      $$ f rightarrow 2 int_{0}^{1}f(x) e^{ipi Jx} dx $$



      Gives the coefficient $a_{j,0}$ of our series.



      Suppose we have no guarantees about non-zero $U_r$ how could we systematically determine the $a_{j,r}$ coefficients of our series?







      complex-analysis fourier-analysis recurrence-relations






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      share|cite|improve this question













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      edited Jan 24 at 23:37









      Bernard

      123k741116




      123k741116










      asked Jan 24 at 23:33









      frogeyedpeasfrogeyedpeas

      7,59972054




      7,59972054






















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