Fix the bug: "M2_i = M1_mat", which was causing the problems getting systemtests to pass.
Removed the specifications of which dtype, the initial matrices are created.
They can be converted later, with the specification of dtype to matrix_exponential_rankN().
All systemtests now pass.
Task #7807 (https://gna.org/task/index.php?7807): Speed-up of dispersion models for Clustered analysis.
