# Getting error as Drift and volatility rates must be specified.

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vetri veeran on 18 Nov 2014
Commented: Barbara Pogacar on 12 Mar 2015
This is my code given below,
Cm=0.01; % Membrane Capcitance uF/cm^2 dt=0.04; % Time Step ms t=0:dt:25; %Time Array ms I=0.1; %External Current Applied
ENa=55.17; % mv Na reversal potential EK=-72.14; % mv K reversal potential El=-49.42; % mv Leakage reversal potential
gbarNa=1.2; % mS/cm^2 Na conductance gbarK=0.36; % mS/cm^2 K conductance gbarl=0.003 % mS/cm^2 Leakage conductance
V(1)=-60; % Initial Membrane voltage m(1)=am(V(1))/(am(V(1))+bm(V(1))); % Initial m-value n(1)=an(V(1))/(an(V(1))+bn(V(1))); % Initial n-value h(1)=ah(V(1))/(ah(V(1))+bh(V(1))); % Initial h-value
for i=1:length(t)-1
%Euler method to find the next m/n/h value m(i+1)=m(i)+dt*((am(V(i))*(1-m(i)))-(bm(V(i))*m(i))); n(i+1)=n(i)+dt*((an(V(i))*(1-n(i)))-(bn(V(i))*n(i))); h(i+1)=h(i)+dt*((ah(V(i))*(1-h(i)))-(bh(V(i))*h(i))); gNa=gbarNa*m(i)^3*h(i); gK=gbarK*n(i)^4; gl=gbarl; INa=gNa*(V(i)-ENa); IK=gK*(V(i)-EK); Il=gl*(V(i)-El);
%Euler method to find the next voltage value
V(i+1)=V(i)+(dt)*((1/Cm)*(I-(INa+IK+Il)));
end
%Store variables for graphing later FE=V; FEm=m; FEn=n; FEh=h;
clear V m n h;
Sub Functions used are given below
function a=am(v) %Alpha for Variable m a=0.1*(v+35)/(1-exp(-(v+35)/10)); end function b=bm(v) %Beta for variable m b=4.0*exp(-0.0556*(v+60)); end function a=an(v)%Alpha for variable n a=0.01*(v+50)/(1-exp(-(v+50)/10)); end function b=bn(v) %Beta for variable n b=0.125*exp(-(v+60)/80); end function a=ah(v) %Alpha value for variable h a=0.07*exp(-0.05*(v+60)); end function b =bh(v) %beta value for variable h b=1/(1+exp(-(0.1)*(v+30))); end
I am getting an error as,
Error using bm (line 140) Drift and volatility rates must be specified.
Error in fwdeuler (line 26) m(1)=am(V(1))/(am(V(1))+bm(V(1))); % Initial m-value
Please Can somebody help me to overcome this error
Thank you.
##### 2 CommentsShowHide 1 older comment
Barbara Pogacar on 12 Mar 2015
OK yes, you must rename bm...for example replace all bm with betam, or some other name, and it will work

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