Integration methods

Which integration methods are currently implemented in gnucap's 
transient analysis? As far as I can see, only trapezoid and 
backward-euler is present (e_storag.cc), and gear method falls back to 
euler. Is there any plan to extend this set?

Also, I would like to hack some other algorithms. How to test the 
correctness and performance of the integration method? Is there any 
testbench available reliably exercising integration accuracy and 
stability? If not, how to isolate this part of analysis? I.e. how to 
kill time-step control and save all transient simulation data.

Regards,
Andrzej