When I use MatlabR2016a change the ".m" file to C++ or C code some errors occured. I use the method"mex -setup C++". When "Checking for Issiues" ,something wrong in "Generating trial code" like: Undefined function or variable.

Undefined function or variable "Dxy". The first assignment to a local variable determines its class.

[José-Luis]

You'd make it easier for people to help if you posted a minimum working example that reproduces your problem.

Otherwise, the error message is pretty straightforward. Dxy doesn't exist and you are trying to do something with it.