functions: correct BesselBase._eval_expand_func() helper

Closes sympy/sympy#21486
skirpichev · Jun 2, 2021 · 7fe2706 · 7fe2706
1 parent b7cbfcf
commit 7fe2706
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diff --git a/diofant/functions/special/bessel.py b/diofant/functions/special/bessel.py
@@ -70,7 +70,7 @@ def _eval_conjugate(self):
 
     def _eval_expand_func(self, **hints):
         nu, z, f = self.order, self.argument, self.__class__
-        if nu.is_extended_real:
+        if nu.is_real:
             if (nu - 1).is_positive:
                 return (-self._a*self._b*f(nu - 2, z)._eval_expand_func() +
                         2*self._a*(nu - 1)*f(nu - 1, z)._eval_expand_func()/z)

diff --git a/diofant/tests/functions/test_bessel.py b/diofant/tests/functions/test_bessel.py
@@ -173,6 +173,10 @@ def check(eq, ans):
         assert besselx(i, x).is_extended_real is None
         assert besselx(x, z).is_extended_real is None
 
+        # issue sympy/sympy#21486
+        assert expand_func(besselx(oo, x)) == besselx(oo, x, evaluate=False)
+        assert expand_func(besselx(-oo, x)) == besselx(-oo, x, evaluate=False)
+
     for besselx in [besselj, besseli]:
         assert besselx(i, r).is_extended_real
     for besselx in [bessely, besselk]:

diff --git a/docs/release/notes-0.13.rst b/docs/release/notes-0.13.rst
@@ -85,3 +85,4 @@ These Sympy issues also were addressed:
 * :sympyissue:`21460`: Polynomial GCD result is different for dense trivial polynomial
 * :sympyissue:`21466`: Regression for match for differential binomial expression
 * :sympyissue:`21166`: Wrong integration result involving square root of absolute value
+* :sympyissue:`21486`: expand_func(besselj(oo, x)) -> RecursionError