Less Than and Less Than or Equal to Not Working Properly

20 views (last 30 days)
I was wondeirng if anyone could look at my function and see what is going on with the <= and < portions of my if/else statement. The statement is defining Is to be 200 from [0, .15), yet it is being definied as 200 from (0, .15]. Effectively, it's reading the <= as <, and the < as <=. Additionally, if anyone could explain why the table is starting at -.15 even though -.2 is the specified starting point, it would be very helpful. Any help would be appreciated, thanks.
clear all
% Set parameters (constants)
tStart = -.200 ; % start time, millisec
tEnd = .200 ; % end time, millisec
deltaT = 0.050 ; % time step, millisec
nStep = ceil((tEnd-tStart)/deltaT) ; % number of time steps
outputInterval = 20 ; % number of time steps between screen output
Vrest = -60 ; % resting potential, mV
EK = -72.1 ; % potassium Nernst potential, mV
ENa = 52.4 ; % sodium Nernst potential, mV
EL = -49.2 ; % leak Nernst potential, mV
gK_max = 36 ; % potassium saturation conductance, mS/cm^2
gNa_max = 120 ; % sodium saturation conductance, mS/cm^2
gL_max = 0.3 ; % leak saturation conductance, mS/cm^2
Cm = 1 ; % Membrane Capacitance
Jstim = 200 ;
StimDur = .15 ;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Set initial value of state variables
Vm = Vrest ; % membrane potential, mV
n = 0.31768 ; % initial value of n gate
m = 0.05293 ; % initial value of m gate
h = 0.59612 ; % initial value of h gate
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Preallocate storage for variables to plot
plot_Vm = zeros(nStep,1) ;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Print a heading for the screen output
disp('Hodgkin-Huxley squid giant axon model')
disp(' i time Jion Vm dVdt n m h')
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Start the simulation
tNow = tStart ;
for iStep = 1:nStep
% Compute ion currents at tNow, then apply stimulus current
if (0<=tNow && tNow<StimDur) % start stimulus current at tNow=0
Is = Jstim ;
else % stop stimulus when tNow = StimDur
Is = 0 ;
end
JNa = gNa_max.*m.^3.*h.*(Vm-ENa) ;
JK = gK_max.*n.^4.*(Vm-EK) ;
JL = gL_max.*(Vm-EL);
Jion = JNa+JK+JL
Vdot = (Is-Jion)./Cm
% Compute gates' opening and closing rates
[a_n, b_n] = get_n_rates(Vm)
[a_m, b_m] = get_m_rates(Vm)
[a_h, b_h] = get_h_rates(Vm)
% Compute change in state variables
deltaVm = (Is - JNa - JK - JL)./Cm .* deltaT ;
delta_m = (a_m.*(1-m) - b_m.*(m)) .* deltaT ;
delta_n = (a_n.*(1-n) - b_n.*(n)) .* deltaT ;
delta_h = (a_h.*(1-h) - b_h.*(h)) .* deltaT ;
if mod(iStep,outputInterval) == 0
fprintf('%5d %8.2f %8.3f %7.3f %7.2f %7.5f %7.5f %7.5f\n', ...
iStep, tNow, Jion, Vm, dV_dt, n, m, h) ;
end % if mod(tNow)
%Update State Veriable
Vm = Vm + deltaVm ;
m = m + delta_m
n = n + delta_n
h = h + delta_h
tNow = tStart + iStep.*deltaT
% Update state variables
iStepAll(iStep) = iStep;
tNowAll(iStep) = tNow;
IsAll(iStep) = Is;
VmAll(iStep) = Vm
VdotAll(iStep) =Vdot;
nAll(iStep) = n;
mAll(iStep) = m;
hAll(iStep) = h;
end % for iStep
% end of file
T = table (iStepAll', tNowAll', IsAll', VmAll', VdotAll', nAll', mAll', hAll', 'VariableNames', ["LoopCnt", "Time", "Is", "Vm", "Vdot", "n", "m", "h"] )
  3 Comments
Michael Van de Graaff
Michael Van de Graaff on 16 Dec 2021
Can you slim this down to somehting that isolates the problem? I don't have get_n_rates() so i don't know what its doing because it throws an error before finishing the first loop
also, you say you want Is be 200 from [0, 0.15) But I don't know what this means in MATLAB, it looks like half open interval notation, but I don't know how to interpret that as a MATLAB array.

Sign in to comment.

Accepted Answer

Michael Van de Graaff
Michael Van de Graaff on 16 Dec 2021
So, for the part of your question "Additionally, if anyone could explain why the table is starting at -.15 even though -.2 is the specified starting point, it would be very helpful."
at the end of the first iteration, you have
tNowAll(iStep) = tNow;
But this is after you've incremented tNow
tNow = tStart + iStep.*deltaT
% Update state variables
iStepAll(iStep) = iStep;
tNowAll(iStep) = tNow; % for iStep = 1, this is tStart+deltaT
so move those assignments prior to the increment
  2 Comments
Star Strider
Star Strider on 16 Dec 2021
It’s possible that the equalities aren’t working becasue of floating-point approximation error.
See the documentation section on Floating-Point Numbers for an extended discussion.
This was also recently discussed in detail in Why doesn't 'find' function work properly?
.

Sign in to comment.

More Answers (0)

Products


Release

R2021a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!