SDIRK solver convergence

[maqsoodrajput]

I am trying to check if the SDIRK solvers in kpp/int/ (with fixed step-size) give correct order of convergence. In all cases (second/third/fourth order solver) I am getting an order ~1 which is strange.

[RolfSander]

I'm not familiar with SDIRK. I almost always use the Rosenbrock integrator. Anyway, how do you determine the order of convergence? Is there a variable in sdirk.f90, or are you calculating it yourself?