Error with indexing an array "Subscript indices must either be real positive integers or logicals"

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Having trouble swapping different equations into a Runge-Kutta 4 ode solver for coupled equations.

Any idea as to what is going on with my index, i?

I made sure to take the ceiling of the ending value, N, but not sure what else is happening..

Subscript indices must either be real positive integers or logicals.
Error in RungeKutta4FitzhughNagumo>@(t,V,W)epsilon(V-gamma*W)
Error in RungeKutta4FitzhughNagumo (line 32)
    k1W=fW(t(i)     ,V(i),          W(i)        );
% dV/dt = f(v + veq) - f(veq) - w    % Potential
% dW/dt = epsilon(v - gamma*w)   % sodium gating variable
clear; clc
% constants
a=0.139;
epsilon=0.008;
gamma=2.54;
veq=0.07;
% Define function dandles
fV=@(t,V,W) (V + veq)*((V + veq)-a)*(1-(V + veq)) - veq*(veq-a)*(1-veq) - W;
fW=@(t,V,W) epsilon(V - gamma*W);
% initial conditions
t(1) = 0;
V(1) = 1;
W(1) = 1;
% Step size
h=0.1;
tfinal=50;
N=ceil(tfinal/h);
fprintf('"N = %d"',N);
% Update loop
for i=1:N
    fprintf('"i = %d"',i);
    %update time
    t(i+1)=t(i)+h;
    % Update & F
    k1R=fV(t(i)     ,V(i),          W(i)        );
    k1W=fW(t(i)     ,V(i),          W(i)        );
      k2V=fV(t(i)+h/2 ,V(i)+h/2*k1V,  W(i)+h/2*k1W);
      k2W=fW(t(i)+h/2 ,V(i)+h/2*k1V,  W(i)+h/2*k1W);
      k3V=fV(t(i)+h/2 ,V(i)+h/2*k2V,  W(i)+h/2*k2W);
      k3W=fW(t(i)+h/2 ,V(i)+h/2*k2V,  W(i)+h/2*k2W);
      k4V=fV(t(i)+h/2 ,V(i)+h  *k3V,  W(i)+h  *k3W);
      k4W=fW(t(i)+h/2 ,V(i)+h  *k4V,  W(i)+h  *k3W);
      V(i+1)=V(i) + h/6*(k1R + 2*k2V + 2*k3V + k4V);
      W(i+1)=W(i) + h/6*(k1W + 2*k2W + 2*k3W + k4W);
  end   
      %plot the solution
      figure(1); clf(1)
      plot(t,V)
      hold on
      plot(t,W)
      xlabel('Time')
      ylabel('Populations')
      legend('Rabits','Foxes')
      set(gca,'FontSize',16)