how to multiply matrix except diagonal matrix

[adik1310]

i make a project for improving fault analysis by using sequence components, and i use C++. now i have problem how to multiply that matrix with angle 30 degree but not affected diagonal matrix. i.e y11,y22,y33 etc.

[arnaudk]

It sounds like you're trying to do an SO(3) rotation, the exact parameterization of this depends on the basis of your matrix. In an orthonormal Eucledian basis, rotation in any arbitrary direction can be accomplished using 3 Euler angles; the parameterization of the determinant 1 matrix which does this can be found here. To implement matrix algebra in C/C++, you might want to take a look at the GNU Scientific Library (GSL) or the uBLAS library which is part of boost.

Arnaud