NMODL: Remove unused/unnecessary legacy SOLVE methods in NEURON

[pramodk]

Today, NMODL specification allows the following SOLVE method:

• cnexp
• euler
• derivimplicit
• sparse
• runge
• after_cvode
• adams
• adeuler
• heun
• adrunge
• gear
• simplex
• simeq
• seidel
• clsoda
• cvode_t
• cvode_v

If I look at usage in entire ModelDB models then the following are the usage stats (number of MOD files where that solver method is used, Solver Name):

   5  METHOD <empty>
  24  METHOD after
2421  METHOD cnexp
  15  METHOD cvode
 249  METHOD derivimplicit
  90  METHOD euler
   3  METHOD runge
 381  METHOD sparse

Four years when we discussed this in the context of new NMODL implementation then we decided to only implement: cnexp euler, sparse, derivimplicit

So the question is, which solver methods we can remove from NEURON? This will not only help with code simplification and maintenance but also implementation in new NMODL code generation.

@nrnhines @ramcdougal : could you take a look and which are safe to remove from 9.0?

relevant ticket in NMODL: BlueBrain/nmodl/issues/958

[nrnhines]

Here are the ones to keep

cnexp
euler
derivimplicit
sparse
runge
after_cvode
simeq
cvode_t
cvode_v

[pramodk]

thank you, Michael!

@alkino : Here is the list to delete:

• adams
• adeuler
• heun
• adrunge
• gear
• simplex
• seidel
• clsoda

For the following ones we have to see if we are covering them under our CI. But this could be a separate issue:

• runge
• after_cvode
• simeq
• cvode_t
• cvode_v

[alkino]

You say to remove adrunge but this is the default one if no method is given. Which one should I choose now?

[nrnhines]

derivimplicit should be chosen.

[alexsavulescu]

adams is used in acc. no. 12631 https://github.com/ModelDBRepository/12631/blob/master/IT_wang.mod#L64

Should we reinstate it?