Merge pull request #1062 from brian-team/fix_#1061

Correctly deal with -inf in equations

brian2/core/functions.py

@@ -6,6 +6,7 @@
 import sympy
 from numpy.random import randn, rand
 from sympy import Function as sympy_Function
+from sympy import S
 
 import brian2.units.unitsafefunctions as unitsafe
 from brian2.core.preferences import prefs
@@ -644,4 +645,7 @@ def timestep(t, dt):
 
 DEFAULT_CONSTANTS = {'pi': SymbolicConstant('pi', sympy.pi, value=np.pi),
                      'e': SymbolicConstant('e', sympy.E, value=np.e),
-                     'inf': SymbolicConstant('inf', sympy.oo, value=np.inf)}
+                     'inf': SymbolicConstant('inf', S.Infinity,
+                                             value=np.inf),
+                     '-inf': SymbolicConstant('-inf', S.NegativeInfinity,
+                                              value=-np.inf)}

brian2/tests/test_parsing.py

@@ -476,6 +476,13 @@ def test_error_messages():
             assert expected_2 in message
 
 
+@attr('codegen-independent')
+def test_sympy_infinity():
+    # See github issue #1061
+    assert sympy_to_str(str_to_sympy('inf')) == 'inf'
+    assert sympy_to_str(str_to_sympy('-inf')) == '-inf'
+
+
 if __name__=='__main__':
     test_parse_expressions_python()
     test_parse_expressions_numpy()
@@ -493,3 +500,5 @@ def test_error_messages():
     test_substitute_abstract_code_functions()
     test_sympytools()
     test_error_messages()
+    test_sympy_infinity()
+