the variable m_pMatriz is double* and the GetElement and SetElement are methods for CMatrix types
But those functions take and return doubles, so there should be no problem.
They're used fine in some contexts already anyway.
I've attached your code with Set/Get used in many more places, and it compiles fine here.
The //!! comments are what my g++ compiler spotted with
$ g++ -c -W -Wall -ansi -pedantic -O2 foo.cpp

Oh, you might want to rename all your loop variables from i,j to be say r,c to denote row and column. It's not always clear whether you're accessing the correct element of the array (when you're doing it directly), and r/c would make it more readable IMO.

At least by always using the set/get functions, every access is properly range checked (as it should be).