Analytic continuation of the incomplete beta function











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Is there a rigorous proof for the analytic continuation of the incomplete beta function $B(x;a,b)$ for all values of $a$ and $b$? The incomplete beta function normally restricts the values of $a,b$ as $a>0$, $b>0$. So I would like to extend these values to negative but I cannot find a good and comprehensive reference for this.



There is a given expression in wikipedia for the analytic continuation of beta function but I cannot see one for the incomplete one. By the way, the integral that I am working on is:



$$rho=frac{b_0}{1-q}int_0^{1-(b_0/x)^{1-q}}v^{-1/2}(1-v)^{frac{1}{q-1}-1}dv=frac{b_0}{1-q}Beta(1-(b_0/x)^{1-q};frac{1}{2},frac{1}{q-1})$$



And I am working on $-infty<q<1$. Thanks for the help.










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    up vote
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    down vote

    favorite












    Is there a rigorous proof for the analytic continuation of the incomplete beta function $B(x;a,b)$ for all values of $a$ and $b$? The incomplete beta function normally restricts the values of $a,b$ as $a>0$, $b>0$. So I would like to extend these values to negative but I cannot find a good and comprehensive reference for this.



    There is a given expression in wikipedia for the analytic continuation of beta function but I cannot see one for the incomplete one. By the way, the integral that I am working on is:



    $$rho=frac{b_0}{1-q}int_0^{1-(b_0/x)^{1-q}}v^{-1/2}(1-v)^{frac{1}{q-1}-1}dv=frac{b_0}{1-q}Beta(1-(b_0/x)^{1-q};frac{1}{2},frac{1}{q-1})$$



    And I am working on $-infty<q<1$. Thanks for the help.










    share|cite|improve this question


























      up vote
      0
      down vote

      favorite









      up vote
      0
      down vote

      favorite











      Is there a rigorous proof for the analytic continuation of the incomplete beta function $B(x;a,b)$ for all values of $a$ and $b$? The incomplete beta function normally restricts the values of $a,b$ as $a>0$, $b>0$. So I would like to extend these values to negative but I cannot find a good and comprehensive reference for this.



      There is a given expression in wikipedia for the analytic continuation of beta function but I cannot see one for the incomplete one. By the way, the integral that I am working on is:



      $$rho=frac{b_0}{1-q}int_0^{1-(b_0/x)^{1-q}}v^{-1/2}(1-v)^{frac{1}{q-1}-1}dv=frac{b_0}{1-q}Beta(1-(b_0/x)^{1-q};frac{1}{2},frac{1}{q-1})$$



      And I am working on $-infty<q<1$. Thanks for the help.










      share|cite|improve this question















      Is there a rigorous proof for the analytic continuation of the incomplete beta function $B(x;a,b)$ for all values of $a$ and $b$? The incomplete beta function normally restricts the values of $a,b$ as $a>0$, $b>0$. So I would like to extend these values to negative but I cannot find a good and comprehensive reference for this.



      There is a given expression in wikipedia for the analytic continuation of beta function but I cannot see one for the incomplete one. By the way, the integral that I am working on is:



      $$rho=frac{b_0}{1-q}int_0^{1-(b_0/x)^{1-q}}v^{-1/2}(1-v)^{frac{1}{q-1}-1}dv=frac{b_0}{1-q}Beta(1-(b_0/x)^{1-q};frac{1}{2},frac{1}{q-1})$$



      And I am working on $-infty<q<1$. Thanks for the help.







      beta-function analytic-continuation






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      edited Nov 21 at 14:47









      Klangen

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      asked Aug 21 at 3:40









      user583893

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          There is the general complete description with the regularized Gauss hypergeometric function ${{_2}tilde{F}_{1}}(a,b,c,x)$, see 1 and 2: $$
          B_x(a,b)= Gamma(a),x^a ;{{_2}tilde{F}_{1}}(a,1-b,a+1,x), qquad -a notin mathbb{N}
          $$



          When $a le 0$ or $b le 0$, the Gauss hypergeometric function ${{_2}F_{1}}$ function can be used: If $a neq 0$ is no negative integer, the result is (3)
          $$
          B_x(a,b)= frac{x^a}{a},{{_2}F_{1}}(a,1-b,a+1,x), qquad -a notin mathbb{N},
          $$
          else if $b neq 0$ is no negative integer, then (4):
          $$
          B_x(a,b)= B(a,b)- frac{(1-x)^b x^a}{b};{{_2}F_{1}}(1,a+b,b+1,1-x), qquad -b notin mathbb{N}.
          $$






          share|cite|improve this answer





















          • Hi. Thanks for the answer. I don't actually understand this. If the parameter $b$ takes a value of zero or any negative value, I can use the last equation? Is that right?
            – user583893
            Aug 21 at 9:44










          • No, you can use it if $b ne -1, -2, dots$ otherwise $ c= b+1$ becomes zero, and the the Gauss function is undefined. The regularized function $${{_2}tilde{F}_{1}}(a,b,c,x) = frac{1}{Gamma(c)} {{_2}F_{1}}(a,b,c,x)$$ can handle this because together with $Gamma(c)$ you get a finite limit if $c$ approaches a negative integer or zero.
            – gammatester
            Aug 21 at 9:56










          • What i need is what works for negative values of b. I already tried in the mathematica, and it gave me the correct answer.
            – user583893
            Aug 21 at 10:36










          • What i need is an extension of incomplete beta function that works for negative values of the parameter $b$. But i tried feeding up negative values of $b$ to the last equation and it gave me the right answers. Now I am confused since the last equation must only work for positive $b$'s.
            – user583893
            Aug 21 at 10:40










          • No it does work for negative non-integer $b$. If $b$ is a negative integer and $a$ is not you can use the second formula, otherwise use the regularized function. But note the hint given at functions.wolfram.com/GammaBetaErf/Beta3/02/02. Using my own implementation I get for example $B_{0.5}(-1.5, -2.5)= 6.4$ (verified on Wolfram function evaluation).
            – gammatester
            Aug 21 at 10:56











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          up vote
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          down vote



          accepted










          There is the general complete description with the regularized Gauss hypergeometric function ${{_2}tilde{F}_{1}}(a,b,c,x)$, see 1 and 2: $$
          B_x(a,b)= Gamma(a),x^a ;{{_2}tilde{F}_{1}}(a,1-b,a+1,x), qquad -a notin mathbb{N}
          $$



          When $a le 0$ or $b le 0$, the Gauss hypergeometric function ${{_2}F_{1}}$ function can be used: If $a neq 0$ is no negative integer, the result is (3)
          $$
          B_x(a,b)= frac{x^a}{a},{{_2}F_{1}}(a,1-b,a+1,x), qquad -a notin mathbb{N},
          $$
          else if $b neq 0$ is no negative integer, then (4):
          $$
          B_x(a,b)= B(a,b)- frac{(1-x)^b x^a}{b};{{_2}F_{1}}(1,a+b,b+1,1-x), qquad -b notin mathbb{N}.
          $$






          share|cite|improve this answer





















          • Hi. Thanks for the answer. I don't actually understand this. If the parameter $b$ takes a value of zero or any negative value, I can use the last equation? Is that right?
            – user583893
            Aug 21 at 9:44










          • No, you can use it if $b ne -1, -2, dots$ otherwise $ c= b+1$ becomes zero, and the the Gauss function is undefined. The regularized function $${{_2}tilde{F}_{1}}(a,b,c,x) = frac{1}{Gamma(c)} {{_2}F_{1}}(a,b,c,x)$$ can handle this because together with $Gamma(c)$ you get a finite limit if $c$ approaches a negative integer or zero.
            – gammatester
            Aug 21 at 9:56










          • What i need is what works for negative values of b. I already tried in the mathematica, and it gave me the correct answer.
            – user583893
            Aug 21 at 10:36










          • What i need is an extension of incomplete beta function that works for negative values of the parameter $b$. But i tried feeding up negative values of $b$ to the last equation and it gave me the right answers. Now I am confused since the last equation must only work for positive $b$'s.
            – user583893
            Aug 21 at 10:40










          • No it does work for negative non-integer $b$. If $b$ is a negative integer and $a$ is not you can use the second formula, otherwise use the regularized function. But note the hint given at functions.wolfram.com/GammaBetaErf/Beta3/02/02. Using my own implementation I get for example $B_{0.5}(-1.5, -2.5)= 6.4$ (verified on Wolfram function evaluation).
            – gammatester
            Aug 21 at 10:56















          up vote
          1
          down vote



          accepted










          There is the general complete description with the regularized Gauss hypergeometric function ${{_2}tilde{F}_{1}}(a,b,c,x)$, see 1 and 2: $$
          B_x(a,b)= Gamma(a),x^a ;{{_2}tilde{F}_{1}}(a,1-b,a+1,x), qquad -a notin mathbb{N}
          $$



          When $a le 0$ or $b le 0$, the Gauss hypergeometric function ${{_2}F_{1}}$ function can be used: If $a neq 0$ is no negative integer, the result is (3)
          $$
          B_x(a,b)= frac{x^a}{a},{{_2}F_{1}}(a,1-b,a+1,x), qquad -a notin mathbb{N},
          $$
          else if $b neq 0$ is no negative integer, then (4):
          $$
          B_x(a,b)= B(a,b)- frac{(1-x)^b x^a}{b};{{_2}F_{1}}(1,a+b,b+1,1-x), qquad -b notin mathbb{N}.
          $$






          share|cite|improve this answer





















          • Hi. Thanks for the answer. I don't actually understand this. If the parameter $b$ takes a value of zero or any negative value, I can use the last equation? Is that right?
            – user583893
            Aug 21 at 9:44










          • No, you can use it if $b ne -1, -2, dots$ otherwise $ c= b+1$ becomes zero, and the the Gauss function is undefined. The regularized function $${{_2}tilde{F}_{1}}(a,b,c,x) = frac{1}{Gamma(c)} {{_2}F_{1}}(a,b,c,x)$$ can handle this because together with $Gamma(c)$ you get a finite limit if $c$ approaches a negative integer or zero.
            – gammatester
            Aug 21 at 9:56










          • What i need is what works for negative values of b. I already tried in the mathematica, and it gave me the correct answer.
            – user583893
            Aug 21 at 10:36










          • What i need is an extension of incomplete beta function that works for negative values of the parameter $b$. But i tried feeding up negative values of $b$ to the last equation and it gave me the right answers. Now I am confused since the last equation must only work for positive $b$'s.
            – user583893
            Aug 21 at 10:40










          • No it does work for negative non-integer $b$. If $b$ is a negative integer and $a$ is not you can use the second formula, otherwise use the regularized function. But note the hint given at functions.wolfram.com/GammaBetaErf/Beta3/02/02. Using my own implementation I get for example $B_{0.5}(-1.5, -2.5)= 6.4$ (verified on Wolfram function evaluation).
            – gammatester
            Aug 21 at 10:56













          up vote
          1
          down vote



          accepted







          up vote
          1
          down vote



          accepted






          There is the general complete description with the regularized Gauss hypergeometric function ${{_2}tilde{F}_{1}}(a,b,c,x)$, see 1 and 2: $$
          B_x(a,b)= Gamma(a),x^a ;{{_2}tilde{F}_{1}}(a,1-b,a+1,x), qquad -a notin mathbb{N}
          $$



          When $a le 0$ or $b le 0$, the Gauss hypergeometric function ${{_2}F_{1}}$ function can be used: If $a neq 0$ is no negative integer, the result is (3)
          $$
          B_x(a,b)= frac{x^a}{a},{{_2}F_{1}}(a,1-b,a+1,x), qquad -a notin mathbb{N},
          $$
          else if $b neq 0$ is no negative integer, then (4):
          $$
          B_x(a,b)= B(a,b)- frac{(1-x)^b x^a}{b};{{_2}F_{1}}(1,a+b,b+1,1-x), qquad -b notin mathbb{N}.
          $$






          share|cite|improve this answer












          There is the general complete description with the regularized Gauss hypergeometric function ${{_2}tilde{F}_{1}}(a,b,c,x)$, see 1 and 2: $$
          B_x(a,b)= Gamma(a),x^a ;{{_2}tilde{F}_{1}}(a,1-b,a+1,x), qquad -a notin mathbb{N}
          $$



          When $a le 0$ or $b le 0$, the Gauss hypergeometric function ${{_2}F_{1}}$ function can be used: If $a neq 0$ is no negative integer, the result is (3)
          $$
          B_x(a,b)= frac{x^a}{a},{{_2}F_{1}}(a,1-b,a+1,x), qquad -a notin mathbb{N},
          $$
          else if $b neq 0$ is no negative integer, then (4):
          $$
          B_x(a,b)= B(a,b)- frac{(1-x)^b x^a}{b};{{_2}F_{1}}(1,a+b,b+1,1-x), qquad -b notin mathbb{N}.
          $$







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Aug 21 at 8:16









          gammatester

          16.6k21631




          16.6k21631












          • Hi. Thanks for the answer. I don't actually understand this. If the parameter $b$ takes a value of zero or any negative value, I can use the last equation? Is that right?
            – user583893
            Aug 21 at 9:44










          • No, you can use it if $b ne -1, -2, dots$ otherwise $ c= b+1$ becomes zero, and the the Gauss function is undefined. The regularized function $${{_2}tilde{F}_{1}}(a,b,c,x) = frac{1}{Gamma(c)} {{_2}F_{1}}(a,b,c,x)$$ can handle this because together with $Gamma(c)$ you get a finite limit if $c$ approaches a negative integer or zero.
            – gammatester
            Aug 21 at 9:56










          • What i need is what works for negative values of b. I already tried in the mathematica, and it gave me the correct answer.
            – user583893
            Aug 21 at 10:36










          • What i need is an extension of incomplete beta function that works for negative values of the parameter $b$. But i tried feeding up negative values of $b$ to the last equation and it gave me the right answers. Now I am confused since the last equation must only work for positive $b$'s.
            – user583893
            Aug 21 at 10:40










          • No it does work for negative non-integer $b$. If $b$ is a negative integer and $a$ is not you can use the second formula, otherwise use the regularized function. But note the hint given at functions.wolfram.com/GammaBetaErf/Beta3/02/02. Using my own implementation I get for example $B_{0.5}(-1.5, -2.5)= 6.4$ (verified on Wolfram function evaluation).
            – gammatester
            Aug 21 at 10:56


















          • Hi. Thanks for the answer. I don't actually understand this. If the parameter $b$ takes a value of zero or any negative value, I can use the last equation? Is that right?
            – user583893
            Aug 21 at 9:44










          • No, you can use it if $b ne -1, -2, dots$ otherwise $ c= b+1$ becomes zero, and the the Gauss function is undefined. The regularized function $${{_2}tilde{F}_{1}}(a,b,c,x) = frac{1}{Gamma(c)} {{_2}F_{1}}(a,b,c,x)$$ can handle this because together with $Gamma(c)$ you get a finite limit if $c$ approaches a negative integer or zero.
            – gammatester
            Aug 21 at 9:56










          • What i need is what works for negative values of b. I already tried in the mathematica, and it gave me the correct answer.
            – user583893
            Aug 21 at 10:36










          • What i need is an extension of incomplete beta function that works for negative values of the parameter $b$. But i tried feeding up negative values of $b$ to the last equation and it gave me the right answers. Now I am confused since the last equation must only work for positive $b$'s.
            – user583893
            Aug 21 at 10:40










          • No it does work for negative non-integer $b$. If $b$ is a negative integer and $a$ is not you can use the second formula, otherwise use the regularized function. But note the hint given at functions.wolfram.com/GammaBetaErf/Beta3/02/02. Using my own implementation I get for example $B_{0.5}(-1.5, -2.5)= 6.4$ (verified on Wolfram function evaluation).
            – gammatester
            Aug 21 at 10:56
















          Hi. Thanks for the answer. I don't actually understand this. If the parameter $b$ takes a value of zero or any negative value, I can use the last equation? Is that right?
          – user583893
          Aug 21 at 9:44




          Hi. Thanks for the answer. I don't actually understand this. If the parameter $b$ takes a value of zero or any negative value, I can use the last equation? Is that right?
          – user583893
          Aug 21 at 9:44












          No, you can use it if $b ne -1, -2, dots$ otherwise $ c= b+1$ becomes zero, and the the Gauss function is undefined. The regularized function $${{_2}tilde{F}_{1}}(a,b,c,x) = frac{1}{Gamma(c)} {{_2}F_{1}}(a,b,c,x)$$ can handle this because together with $Gamma(c)$ you get a finite limit if $c$ approaches a negative integer or zero.
          – gammatester
          Aug 21 at 9:56




          No, you can use it if $b ne -1, -2, dots$ otherwise $ c= b+1$ becomes zero, and the the Gauss function is undefined. The regularized function $${{_2}tilde{F}_{1}}(a,b,c,x) = frac{1}{Gamma(c)} {{_2}F_{1}}(a,b,c,x)$$ can handle this because together with $Gamma(c)$ you get a finite limit if $c$ approaches a negative integer or zero.
          – gammatester
          Aug 21 at 9:56












          What i need is what works for negative values of b. I already tried in the mathematica, and it gave me the correct answer.
          – user583893
          Aug 21 at 10:36




          What i need is what works for negative values of b. I already tried in the mathematica, and it gave me the correct answer.
          – user583893
          Aug 21 at 10:36












          What i need is an extension of incomplete beta function that works for negative values of the parameter $b$. But i tried feeding up negative values of $b$ to the last equation and it gave me the right answers. Now I am confused since the last equation must only work for positive $b$'s.
          – user583893
          Aug 21 at 10:40




          What i need is an extension of incomplete beta function that works for negative values of the parameter $b$. But i tried feeding up negative values of $b$ to the last equation and it gave me the right answers. Now I am confused since the last equation must only work for positive $b$'s.
          – user583893
          Aug 21 at 10:40












          No it does work for negative non-integer $b$. If $b$ is a negative integer and $a$ is not you can use the second formula, otherwise use the regularized function. But note the hint given at functions.wolfram.com/GammaBetaErf/Beta3/02/02. Using my own implementation I get for example $B_{0.5}(-1.5, -2.5)= 6.4$ (verified on Wolfram function evaluation).
          – gammatester
          Aug 21 at 10:56




          No it does work for negative non-integer $b$. If $b$ is a negative integer and $a$ is not you can use the second formula, otherwise use the regularized function. But note the hint given at functions.wolfram.com/GammaBetaErf/Beta3/02/02. Using my own implementation I get for example $B_{0.5}(-1.5, -2.5)= 6.4$ (verified on Wolfram function evaluation).
          – gammatester
          Aug 21 at 10:56


















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