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# How do I create variable vectors with a new value for each iteration of a loop?

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Ragini Ravichandren on 5 Apr 2021
Commented: darova on 5 Apr 2021
I wrote the following function, where t and y are supposed to give values for each iteration of the Euler method. However, I don't know how to properly allocate space for the values, nor ensure that the values change and are added to a 1Xn array for each iteration of the loop. Thanks!
function [t,y]=eulerMethod(f3, dt, Tf, t0, y0)
n=(Tf-t0)/dt;
nf=round(n,1);
y= zeros(1, nf);
yp = zeros(1, nf);
yn = zeros(1, nf);
tp= zeros(1, nf);
yp=y0;
tp(n+1,:);
for n=0:nf
tp(n+1)=t0+n*dt;
f3p(n+1)=f3(tp(n+1),yp(n+1));
yn(n+1)=yp(n+1)+dt*f3p(n+1);
yp(n+1) = yn(n+1);
end
t=tp;
y=yp;
end
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### Accepted Answer

darova on 5 Apr 2021
Here are some corrections
% yp=y0; % you are replacing variable yp with y0
yp(1) = y0; % you need to replace first value only
corrections2
tp= zeros(1, nf); % length of array nf
for n=1:nf-1 % start from '1' index
tp(n)=t0+n*dt; % you can access tp(n+1). It doesn't exist
f3p(n)=f3(tp(n),yp(n));
yp(n+1) = yp(n) + dt*f3p(n);
%yp(n+1) = yn(n+1); % you don't need yn variable at all
end
##### 2 CommentsShowHide 1 older comment
darova on 5 Apr 2021
Increase size of tp
tp= zeros(1, nf+1); % length of array nf
for n=1:nf % till the end
Modify tp a bit
tp(n)=t0+(n-1)*dt; % you can access tp(n+1). It doesn't exist

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