"Array indices must be positive integers or logical values"

for i=1:n

disp(i)

ti(i+1)=ti(i)+dt;

x1i(i+1)=x1i(i)+dt(V1i(i))

x2i(i+1)=x2i(i)+dt(V2i(i))

Using, this code I get the error message shown in the subject line, even if i change the updating to x1i(i)= ... this doesn't fix the problem.

Any advice?

[Antoni Garcia-Herreros]

Could you provide some more info on what size is your data (n,ti,dt,V1,V2)?

[Rory Thiel]

function [x1i,x2i, ti] = BasicEuler (RHS1,RHS2,initial, t0, tf, dt)
%create arrays for all variables which change over time
ti=zeros(1,1000);
x1i=zeros(1,1000);
x2i=zeros(1,1000);
V1i=zeros(1,1000);
V2i=zeros(1,1000);


ti(1)=t0;
%%define initial conditions (at  time = 0s)
x1i(1)=initial(1);
x2i(1)=initial(2);
V1i(1)=initial(3);
V2i(1)=initial(4);


n=(tf-t0)/dt; %number of loops
i=0;
while max(ti)<tf
    i=i+1;
    ti(i+1)=ti(i)+dt;
    x1i(i+1)=x1i(i)+dt(V1i(i));
    x2i(i+1)=x2i(i)+dt(V2i(i));
    %Continue on to calculate new V1 and V2 using RHS eqs



end

Here I have tried using a while loop instead but this doesn't resolve the issue

Which I am calling with

[x1i, x2i,ti] = BasicEuler (RHS1,RHS2,initial, t0, tf, dt);

after with all the required inputs in the main script

[Rory Thiel]

 x1i(i+1)=x1i(i)+dt*(V1i(i));

Wasn't really a problem with indexing, I missed the * symbol after dt so it thought I was trying to search a dt array which is just a constant variable

Answer 1

[Cris LaPierre]

Your indices must be positive integer values (or logicals), as the error message states. It is therefore most likely either V1i(i) or V2i(i) are not returing an integer value, causing the error about invalid array indices when used to index into your variable dt.

a=1:3;
% This works
a(1)

ans = 1

% your error
a(1.5)

Array indices must be positive integers or logical values.