Avoid errors with STATE variables without DERIVATE block

[pramodk]

• In case of state variables without ODEs or SOLVE block we get
  errors like:

  V not really a STATE; Ie. No differential equation for it
  gNMDA not really a STATE; Ie. No differential equation for it

• Not sure about the "desirable" fix here:

  • should we avoid declaring variables as STATE
  • use workaround of empty SOLVE block like this PR
  • have fix in neuron to avoid this as an error

Tagging @nrnhines for this to discuss.

[nrnhines]

I'm looking into this. I see that the error occurs with NEURON -- VERSION 7.6.7 HEAD (603da174f) 2019-04-19. Also, the now deprecated http://github.com/nrnhines/nrnverify_modeldb never attempted to run this model. That error message has been present since before 2007 [svn r1897] start development of 6.2 which is as old as the git repository goes.

[pramodk]

Ok, thanks michael for checking.

May be I can remove mentioned variables as STATE and turn them into ASSIGN? that might be simpler than empty SOLVE block?

[nrnhines]

I emailed Salvadore. I'm guessing the wrong version of izhi2007.mod inadvertently ended up in the submitted modeldb zip file.

[pramodk]

Ok. For now, I have converted STATE variables to ASSIGN. Let's see what @salvadord says.

[olupton]

@pramodk this PR also needs an entry in the README

[pramodk]

Done!

[pramodk]

I emailed Salvadore. I'm guessing the wrong version of izhi2007.mod inadvertently ended up in the submitted modeldb zip file.

@nrnhines / @salvadord: was there any conclusion on the above? Otherwise, a simple/compatible change with neuron is to just to not have STATE variables but ASSIGNED. Let us know how to proceed here.

[nrnhines]

@pramodk I think changing to ASSIGNED is the best way to proceed.

[salvadord]

@nrnhines @pramodk Sorry for the late reply. Changing to ASSIGNED makes sense. In a later version of this izhikevich mod file we had actually made that change already, see here: https://senselab.med.yale.edu/ModelDB/ShowModel?model=39948&file=/izhikevich_simple_nrn/izhi2007a.mod#tabs-2

[pramodk]

thank you for confirming @salvadord !