Do not call gemm with 0 stride, some blas refuse.

theano/tensor/blas.py

@@ -478,8 +478,9 @@ class GemmRelated(Op):
                 (long int)Ny[1], (long int)Nz[1]);
             %(fail)s;
         }
-// We must not raise an error when Nx[1] == 0. This would disable case
-// that numpy.dot accept.
+
+        // We must not raise an error when Nx[1] == 0. This would disable cases
+        // that numpy.dot accept.
         """
 
     check_strides = """
@@ -526,14 +527,18 @@ class GemmRelated(Op):
 
     compute_strides = """
         /* create appropriate strides for malformed matrices that are row or column
-         * vectors
+         * vectors, or empty matrices.
+         * In that case, the value of the stride does not really matter, but
+         * some versions of BLAS insist that:
+         *  - they are not smaller than the number of elements in the array,
+         *  - they are not 0.
          */
-        sx_0 = (Nx[0] > 1) ? Sx[0]/type_size : Nx[1];
-        sx_1 = (Nx[1] > 1) ? Sx[1]/type_size : Nx[0];
-        sy_0 = (Ny[0] > 1) ? Sy[0]/type_size : Ny[1];
-        sy_1 = (Ny[1] > 1) ? Sy[1]/type_size : Ny[0];
-        sz_0 = (Nz[0] > 1) ? Sz[0]/type_size : Nz[1];
-        sz_1 = (Nz[1] > 1) ? Sz[1]/type_size : Nz[0];
+        sx_0 = (Nx[0] > 1) ? Sx[0]/type_size : (Nx[1] + 1);
+        sx_1 = (Nx[1] > 1) ? Sx[1]/type_size : (Nx[0] + 1);
+        sy_0 = (Ny[0] > 1) ? Sy[0]/type_size : (Ny[1] + 1);
+        sy_1 = (Ny[1] > 1) ? Sy[1]/type_size : (Ny[0] + 1);
+        sz_0 = (Nz[0] > 1) ? Sz[0]/type_size : (Nz[1] + 1);
+        sz_1 = (Nz[1] > 1) ? Sz[1]/type_size : (Nz[0] + 1);
         """
 
     begin_switch_typenum = """
@@ -639,7 +644,7 @@ class GemmRelated(Op):
             self.end_switch_typenum), '')
 
     def build_gemm_version(self):
-        return (8,)
+        return (9,)
 
 class Gemm(GemmRelated):
     """In-place version of matrix-matrix multiplication (with accumulation):