I am trying to build a mex file from C source code. my mexutils.c code contains a function call to bool mxIsDouble(const mxArray *pa); which is declared in matrix.h and is already included in mexutils.c. But while compiling with mex, it says undefined function. another structure that's declared in matrix.h is recognized in mexutils.h i.e. the header is surely found. This is making me confused. please help. I am using win64, Matlab 2016a.