# Model fitting with refractory period **URL:** \ **Category:** Support\ **Tags:** equations\ **Created:** [24 February 2022 19:43 UTC](https://brian.discourse.group/t/model-fitting-with-refractory-period/615 "2022-02-24T19:43:28Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Tuoma](https://avatars.discourse-cdn.com/v4/letter/t/dec6dc/32.png) [@Tuoma](https://brian.discourse.group/u/Tuoma)\ **Post date:** [24 February 2022 19:43 UTC](https://brian.discourse.group/t/model-fitting-with-refractory-period/615/1 "2022-02-24T19:43:29Z")
I’m following the model fitting example of [Tutorial: TraceFitter — Brian2modelfitting 0.3 documentation](https://brian2modelfitting.readthedocs.io/en/stable/introduction/tutorial_hh.html), but I’m using an adaptive exponential model instead of the given HH model. Now I want to introduce also refractory period, but I get an error. Here’s my code: ```auto from brian2modelfitting import * from brian2 import * import pandas as pd inp_trace = pd.read_csv('input_traces_hh.csv', index_col=0).to_numpy() out_trace = pd.read_csv('output_traces_hh.csv', index_col=0).to_numpy() area = 20000*umetre**2 model = '''dv/dt = (gL*(EL-v)+gL*DeltaT*exp((v-VT)/DeltaT) -w + I)/Cm : volt (unless refractory) dw/dt=(a*(v-EL)-w)/tauw : amp gL : siemens (constant) EL : volt (constant) DeltaT : volt (constant) VT : volt (constant) a : siemens (constant) tauw : second (constant) wadd : ampere (constant) vre : volt (constant) Cm : farad (constant) tref : second (constant) ''' opt = NevergradOptimizer() metric = MSEMetric() fitter = TraceFitter(model=model, input_var='I', output_var='v', input=inp_trace * amp, output=out_trace*mV, dt=0.01*ms, n_samples=1000, method='exponential_euler', param_init={'v': -65*mV}, reset='v=vre; w += wadd', threshold='v > 0*mV', refractory='tref') res, error = fitter.fit(n_rounds=10, optimizer=opt, metric=metric, Cm=[100*pfarad,300*pfarad], gL=[2*psiemens, 300*nsiemens], EL=[-90*mV,-40*mV], VT=[-90*mV,-40*mV], DeltaT=[0.1*mV,20*mV], a=[-1.5*nS,3.0*nS], tauw=[1.0*ms,1000.0*ms], vre=[-80*mV,-60*mV], wadd=[-0.2*nA,0.5*nA], tref=[0.0*ms,5.0*ms]) traces = fitter.generate_traces() ``` The code works if I remove “(unless refractory)”, that is, remove the refractory period, but otherwise it gives me a division by zero. Any ideas how to fix this issue? Is refractory period supported at all in brian2modelfitting library? I also seem to get NaNs in the objective function values when I remove “(unless refractory)”, unless I make the length of the refractory period shorter than the simulation time step. ---
**Author:** ![mstimberg](https://yyz2.discourse-cdn.com/free1/user_avatar/brian.discourse.group/mstimberg/32/11_2.png) [@mstimberg](https://brian.discourse.group/u/mstimberg)\ **Post date:** [28 February 2022 14:11 UTC](https://brian.discourse.group/t/model-fitting-with-refractory-period/615/2 "2022-02-28T14:11:36Z")
Hi @Tuoma . Using refractoriness in fitted models should work in principle. The error you are getting is due to a bug, though it seems to be a bug in Brian’s code optimization itself rather than in `brian2modelfitting`. Brian’s code generation simplifies expression by replacing expressions with fixed values, e.g. `1.0 / 2.0` will be replaced by `0.5`. Apparently in this case it tries to replace `1.0 / 0.0` by a value, which leads to the division by zero error. I will have to have a closer look into why this is happening in this specific case, but in the mean time I think you could use the following work-around. Instead of `(unless refractory)`, you use `dv/dt = not_refractory*(gL*....)`, i.e. manually multiply the RHS of the equation by 0 or 1. This is basically what `(unless refractory)` does, even though in general it does a bit more (e.g. discard changes to the membrane potential by synapses) – but this should not matter here. ---
**Author:** ![Tuoma](https://avatars.discourse-cdn.com/v4/letter/t/dec6dc/32.png) [@Tuoma](https://brian.discourse.group/u/Tuoma)\ **Post date:** [28 February 2022 15:27 UTC](https://brian.discourse.group/t/model-fitting-with-refractory-period/615/3 "2022-02-28T15:27:13Z")
Thanks, that seems to work! ---
**Author:** ![mstimberg](https://yyz2.discourse-cdn.com/free1/user_avatar/brian.discourse.group/mstimberg/32/11_2.png) [@mstimberg](https://brian.discourse.group/u/mstimberg)\ **Post date:** [2 March 2022 15:41 UTC](https://brian.discourse.group/t/model-fitting-with-refractory-period/615/4 "2022-03-02T15:41:15Z")
For future reference, this has now been fixed in Brian’s current development version: [Make evaluate\_expr more robust by mstimberg · Pull Request #1389 · brian-team/brian2 · GitHub](https://github.com/brian-team/brian2/pull/1389)