# Problem using ODE45 - current not recognized

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Samuele Bolotta on 6 Mar 2021
Commented: Samuele Bolotta on 6 Mar 2021
I am using this function:
%Constants set
Cm=0.01; % Membrane Capcitance
dt=0.01; % Time Step ms
t=0:dt:25; %Time Array ms
I = zeros (145,1); %Applied constant
I(40:50,1) = 0.1; %Applied constant
V=-60; % Initial Membrane voltage
m=alpham(V)/(alpham(V)+betam(V)); % Initial m-value
n=alphan(V)/(alphan(V)+betan(V)); % Initial n-value
h=alphah(V)/(alphah(V)+betah(V)); % Initial h-value
y0=[V;n;m;h];
tspan = [0,max(t)];
%Matlab's ode45 function
[time,V] = ode45(@ODEMAT,tspan,y0);
OD=V(:,1);
ODn=V(:,2);
ODm=V(:,3);
ODh=V(:,4);
%% Plots
figure
subplot(3,1,1)
plot(time,OD);
legend('ODE45 solver');
xlabel('Time (ms)');
ylabel('Voltage (mV)');
title('Voltage Change for Hodgkin-Huxley Model');
subplot(3,1,2)
plot(time,I);
legend('Current injected')
xlabel('Time (ms)')
ylabel('Ampere')
title('Current')
subplot(3,1,3)
plot(time,[ODn,ODm,ODh]);
legend('ODn','ODm','ODh');
xlabel('Time (ms)')
ylabel('Value')
title('Gating variables')
With ODEMAT being:
function [dydt,I] = ODEMAT(t,y)
%Constants
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
I = zeros (145,1); %Applied constant
I(40:50,1) = 0.1; %Applied constant
Cm = 0.01; % Capacitance
% Values set to equal input values
V = y(1);
n = y(2);
m = y(3);
h = y(4);
gNa = gbarNa*m^3*h;
gK = gbarK*n^4;
gL = gbarl;
INa=gNa*(V-ENa);
IK=gK*(V-EK);
Il=gL*(V-El);
for curr = 1:length(I)
dydt = [((1/Cm)*(I(curr)-(INa+IK+Il))); % This is voltage
alphan(V)*(1-n)-betan(V)*n; %This is gating conductance A
alpham(V)*(1-m)-betam(V)*m; %This is gating conductance B
alphah(V)*(1-h)-betah(V)*h]; %This is gating conductance C
end
end
So what I'm trying to do here is see what happens to voltage and gating conductances when current I switched from 0 to 0.1 (at timestep 40 until 50). However, it looks like the function doesn't really take 0.1 as input, and keeps using 0 instead. Where am I getting it wrong? I also attach the six alpha and beta functions.
Thanks,
Samuele

Star Strider on 6 Mar 2021
I cannot run the posted code:
Unrecognized function or variable 'alpham'.
The others also appear to be missing.
That aside, if ‘I’ is a function of ‘t’, it needs to be stated as such.
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Samuele Bolotta on 6 Mar 2021
Yes sorry, I uploaded the six functions in the zip file. Here they are!