init v=-60

icaf=gca*minf(v)*(v-vca)
aux ica=icaf
# declare the parameters
param vl=-60,vca=120
param i=0,gl=2,gca=4,c=20
param v1=-1.2,v2=18

# user defined functions 
minf(v)=.5*(1+tanh((v-v1)/v2))

# right-hand sides of ODES in order of declaration
v'=(i+gl*(vl-v)-icaf)/c

done