Index exceeds the number of array elements. Index must not exceed 751.

Trying to create a modelling script that will call a variety of modelling techniques to approximate a (relatively simple) ODE. z is the matrix that will store each value for the approximation as the simulation runs.

Here is the code that calls the modelling technique functions from other scripts:

function [t,z] = ivpSolver(t0,z0,dt,tend,dM)
% ivpSolver    Solve an initial value problem (IVP) and plot the result
% 
%     [T,Z] = ivpSolver(T0,Z0,DT,TE) computes the IVP solution using a step 
%     size DT, beginning at time T0 and initial state Z0 and ending at time 
%     TEND. The solution is output as a time vector T and a matrix of state 
%     vectors Z.
% Set initial conditions
t(1) = t0;
z(:,1) = z0;
M(1)=2;
% Continue stepping until the end time is exceeded
n = 1;
while t(n) <= tend
    % Increment the time vector by one time step
    t(n+1) = t(n) + dt;
    
    % Apply Euler's method for one time step
    %[z] = stepEuler(z(:,n), dt, M, dM);
    
    %Apply RK4 method for one time step
    z(:,n+1) = stepRungeKutta(z(:,n), dt, M(n), dM);
    if M(n)>0.5
        M(n+1)=M(n)-(dM*dt);
    end
    n = n + 1;
end

running the code with the command: [t,z] = ivpSolver(0,[10;0],0.1,100,0.02); gives the aforementioned error arrising from line 14: z(:,n+1) = stepRungeKutta(z(:,n), dt, M(n), dM);. Is it not possible to create an array that is longer than 751 columns or is something else causing this error to be displayed?

Answer 1

[VBBV]

 M(n)=M(n)-(dM*dt);

[VBBV]

May be you mean the above. Inside if condition you have incremented M with 1 and outside n gets incremented by 1 again which when passed to stepRungeKutta function produced error. Place the if condition before the function call to stepRungeKutta

[VBBV]

When the if-end condition is not satisfied, variable M have number of elements less by 1, Following the while loop statements, when n is incremented by 1, it will result in error.

[Timothy Dunning]

Thanks a bunch