## What is the numeric integration method of cnexp?

NMODL and the Channel Builder.
gaoyy18
Posts: 11
Joined: Tue Mar 14, 2023 11:33 am

### What is the numeric integration method of cnexp?

Hi,
I see the following codes for HH channel in hh.mod(https://raw.githubusercontent.com/neuro ... noc/hh.mod)

Code: Select all

``````BREAKPOINT {
SOLVE states METHOD cnexp
gna = gnabar*m*m*m*h
ina = gna*(v - ena)
gk = gkbar*n*n*n*n
ik = gk*(v - ek)
il = gl*(v - el)
}
``````
My question for HH channel and cnexp method is:
1. When setting 'secondorder=0' in NEURON scripts, does it mean NEURON will use implicit integration method when iteratively updating both the membrane voltage and voltage-gated variables m, n, h by solving differential equations?
2. if 1 is right, what is the updating sequence for a)membrane voltage and b)voltage-gated variables m, n, h?
The following is my guess, I'm not sure whether it is right, can anyone helps?
1) NEURON will first update a)membrane voltage from v(t) to v(t+1), using b)voltage-gated variables m, n, h at time t(i.e. m(t), n(t), h(t)), using implicit integration method.
2) Then update b)voltage-gated variables m, n, h from m(t), n(t), h(t) to m(t+1), n(t+1), h(t+1), also using implicit integration method.
3) After 1) 2), we get variables at time t+1, and repeat 1) 2)...

It is right or not? Or anyone can help for the correct updating sequence for HH channel？
gaoyy18
Posts: 11
Joined: Tue Mar 14, 2023 11:33 am

### Re: What is the numeric integration method of cnexp?

To anyone who later sees this post:
I got it, cnexp uses analytical integration method instead of numerical method.
ted