changed assertions to error-checking in cuda_ndarray gemm, regarding illegal strides

theano/sandbox/cuda/cuda_ndarray.cu

@@ -2725,7 +2725,8 @@ int CudaNdarray_gemm(float alpha, const CudaNdarray * A, const CudaNdarray * B,
 
     if ((CudaNdarray_HOST_DIMS(A)[1] != CudaNdarray_HOST_DIMS(B)[0])
             || (CudaNdarray_HOST_DIMS(A)[0] != CudaNdarray_HOST_DIMS(C)[0])
-            || (CudaNdarray_HOST_DIMS(B)[1] != CudaNdarray_HOST_DIMS(C)[1]))
+            || (CudaNdarray_HOST_DIMS(B)[1] != CudaNdarray_HOST_DIMS(C)[1])
+            || (CudaNdarray_HOST_DIMS(A)[1] == 0))
     {
         PyErr_Format(PyExc_ValueError, "dimension mismatch in args to gemm (%i,%i)x(%i,%i)->(%i,%i)",
                 CudaNdarray_HOST_DIMS(A)[0],
@@ -2780,12 +2781,22 @@ int CudaNdarray_gemm(float alpha, const CudaNdarray * A, const CudaNdarray * B,
     }
 
     // I don't know if cudablas handles negative strides
-    assert (CudaNdarray_HOST_STRIDES(A)[0] >= 0) ; // for now
-    assert (CudaNdarray_HOST_STRIDES(A)[1] >= 0) ; // for now
-    assert (CudaNdarray_HOST_STRIDES(B)[0] >= 0) ; // for now
-    assert (CudaNdarray_HOST_STRIDES(B)[1] >= 0) ; // for now
-    assert (CudaNdarray_HOST_STRIDES(C)[0] >= 0) ; // for now
-    assert (CudaNdarray_HOST_STRIDES(C)[1] >= 0) ; // for now
+    if (   (CudaNdarray_HOST_STRIDES(A)[0] < 0)
+        || (CudaNdarray_HOST_STRIDES(A)[1] < 0)
+        || (CudaNdarray_HOST_STRIDES(B)[0] < 0)
+        || (CudaNdarray_HOST_STRIDES(B)[1] < 0)
+        || (CudaNdarray_HOST_STRIDES(C)[0] < 0)
+        || (CudaNdarray_HOST_STRIDES(C)[1] < 0))
+    {
+        PyErr_Format(PyExc_ValueError, "illegal strides in args to gemm (%i,%i)x(%i,%i)->(%i,%i)",
+                CudaNdarray_HOST_STRIDES(A)[0],
+                CudaNdarray_HOST_STRIDES(A)[1],
+                CudaNdarray_HOST_STRIDES(B)[0],
+                CudaNdarray_HOST_STRIDES(B)[1],
+                CudaNdarray_HOST_STRIDES(C)[0],
+                CudaNdarray_HOST_STRIDES(C)[1]);
+        return -1;
+    }
 
     /* create appropriate strides for malformed matrices that are row or column
      * vectors