Hello,

I want to use eigen to do some matrix calculations and have a question regarding the fixed size matrices.

The matrix sizes depend on different variables e.g. a,b,c,d. Some matrices have size a+b times a+b, other bc times bc.

a,b,c,d are fixed - but I do not want to write the exact values into the (whole) C code - so I fix them using #define.

Also a+b is calculated by the preprocessor, which makes the Code a bit ackward - I need to define several constant, which are only used to for the sizes of matrices.

Is there a clever way to avoid these many defines?

use const int variables:

const int a = 3;
const int b = 4;

Matrix<float,a+b+1,a*c> mat;

or make them template arguments of your higher level algorithms...

Does that answer your concerns ?

Well, const int can still be overwritten (e.g. with a const_cast), so could theoretically be rejected by compilers, so the way we do it in eigen is as enum values

enum { a = b+c; }