Fix Matlab incompatibility of "ismatrix" (bug #42422). * data.cc (isvector): new tests * data.cc (isrow): documentation improved, new tests * data.cc (iscolumn): documentation improved, new tests * data.cc (ismatrix): is matrix now only checks the dimension due to Matlab compatibility, documentation improved, new tests * accumarray.m: use more appropriate function, than ismatrix * gradient.m: use more appropriate function, than ismatrix * num2str.m: use more appropriate functions, than ismatrix * ntsc2rgb.m: use more appropriate function, than ismatrix * condest.m: use more appropriate function, than ismatrix * expm.m: use more appropriate function, than ismatrix * onenormest.m: use more appropriate function, than ismatrix * isocolors.m: use more appropriate function, than ismatrix * isonormals.m: use more appropriate function, than ismatrix * isosurface.m: use more appropriate function, than ismatrix * __errcomm__.m: use more appropriate function, than ismatrix * __interp_cube__.m: use more appropriate function, than ismatrix * __marching_cube__.m: use more appropriate function, than ismatrix * __stem__.m: use more appropriate function, than ismatrix * stairs.m: use more appropriate function, than ismatrix * validsetargs.m: use more appropriate functions, than ismatrix * unique.m: use more appropriate functions, than ismatrix * bicg.m: additional tests for numerical value * bicgstab.m: additional tests for numerical value * cgs.m: additional tests for numerical value * gmres.m: additional tests for numerical value * qmr.m: additional tests for numerical value

--- a/scripts/general/gradient.m
+++ b/scripts/general/gradient.m
@@ -71,7 +71,7 @@
   endif
 
   nargout_with_ans = max (1,nargout);
-  if (ismatrix (m))
+  if (isnumeric (m))
     [varargout{1:nargout_with_ans}] = matrix_gradient (m, varargin{:});
   elseif (isa (m, "function_handle"))
     [varargout{1:nargout_with_ans}] = handle_gradient (m, varargin{:});