correctly fix the bug discovered by Joseph and added test case.

theano/scalar/basic.py

@@ -171,18 +171,12 @@ class Scalar(Type):
                 ret.imag=0;
                 return ret;
             }
-            complex_type operator =(scalar_type y) {
-                complex_type ret;
-                ret.real=y;
-                ret.imag=0;
-                return ret;
-            }
             %(upcast)s
          };
          """
         # todo: use C templating
         return template % dict(nbits = 64, half_nbits = 32, upcast="") + template % dict(nbits = 128, half_nbits = 64, upcast="""
-        complex_type operator =(npy_float64 y) {
+        complex_type operator =(npy_float32 y) {
                 complex_type ret;
                 ret.real=y;
                 ret.imag=0;

theano/tensor/tests/test_basic.py

@@ -1920,6 +1920,21 @@ def test_sum_overflow():
     f = function([a], sum(a))
     assert f([1]*300) == 300
 
+def test_bug_complext_10_august_09():
+    v0 = dmatrix()
+    v1 = dscalar()
+    v2 = dvector()
+    v3 = dscalar()
+    v5 = sub(v3,v3)
+    v6 = basic.convert_to_complex128(v0)
+#    v7 = basic.convert_to_float64(v6)
+
+    inputs = [v0, v1, v2, v3]
+    outputs = [v5,v6]
+    function(inputs, outputs, mode=compile.Mode('py', 'fast_compile'))
+    function(inputs, outputs, mode=compile.debugmode.DebugMode())
+
+
 if __name__ == '__main__':
     if len(sys.argv) >= 2 and sys.argv[1] == 'OPT':
         default_mode = compile.Mode(linker = 'c&py',