Digital Library of Mathematical Functions
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16 Generalized Hypergeometric Functions and Meijer G-FunctionTwo-Variable Hypergeometric Functions

§16.13 Appell Functions

The following four functions of two real or complex variables x and y cannot be expressed as a product of two \mathop{{{}_{{2}}F_{{1}}}\/}\nolimits functions, in general, but they satisfy partial differential equations that resemble the hypergeometric differential equation (15.10.1):

16.13.1\mathop{{F_{{1}}}\/}\nolimits\!\left(\alpha;\beta,\beta^{{\prime}};\gamma;x,y%
\right)=\sum_{{m,n=0}}^{\infty}\frac{\left(\alpha\right)_{{m+n}}\left(\beta%
\right)_{{m}}\left(\beta^{{\prime}}\right)_{{n}}}{\left(\gamma\right)_{{m+n}}m%
!n!}x^{m}y^{n},\max\left(|x|,|y|\right)<1,
16.13.2\mathop{{F_{{2}}}\/}\nolimits\!\left(\alpha;\beta,\beta^{{\prime}};\gamma,%
\gamma^{{\prime}};x,y\right)=\sum_{{m,n=0}}^{\infty}\frac{\left(\alpha\right)_%
{{m+n}}\left(\beta\right)_{{m}}\left(\beta^{{\prime}}\right)_{{n}}}{\left(%
\gamma\right)_{{m}}\left(\gamma^{{\prime}}\right)_{{n}}m!n!}x^{m}y^{n},|x|+|y|<1,
16.13.3\mathop{{F_{{3}}}\/}\nolimits\!\left(\alpha,\alpha^{{\prime}};\beta,\beta^{{%
\prime}};\gamma;x,y\right)=\sum_{{m,n=0}}^{\infty}\frac{\left(\alpha\right)_{{%
m}}\left(\alpha^{{\prime}}\right)_{{n}}\left(\beta\right)_{{m}}\left(\beta^{{%
\prime}}\right)_{{n}}}{\left(\gamma\right)_{{m+n}}m!n!}x^{m}y^{n},\max\left(|x|,|y|\right)<1,
16.13.4\mathop{{F_{{4}}}\/}\nolimits\!\left(\alpha;\beta;\gamma,\gamma^{{\prime}};x,y%
\right)=\sum_{{m,n=0}}^{\infty}\frac{\left(\alpha\right)_{{m+n}}\left(\beta%
\right)_{{m+n}}}{\left(\gamma\right)_{{m}}\left(\gamma^{{\prime}}\right)_{{n}}%
m!n!}x^{m}y^{n},\sqrt{|x|}+\sqrt{|y|}<1.

Here and elsewhere it is assumed that neither of the bottom parameters \gamma and \gamma^{{\prime}} is a nonpositive integer.