Effacer les filtres
Effacer les filtres

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Subscript indices must either be real positive integers or logicals.

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Harry Price
Harry Price le 1 Déc 2017
Clôturé : MATLAB Answer Bot le 20 Août 2021
I am trying to run eulers method for a first order differential equation. However recieve the above error when I try to plot the results.
See my code blow:
x=zeros(400,1);
y=zeros(400,1);
x(1)=2;
y(1)=4;
for n=1:400
x(n+1)=x(n)+0.005;
y(n+1)=x(n)+0.005.*(((y).^2)+(7*y)+2)/(3*x((y).^2)+((1-x)*(3*((y)^2)+7)));
end
plot(x,y)
title('eulers')
grid on
What am I doing wrong?

Réponses (1)

KL
KL le 1 Déc 2017
when you write,
y(n+1)=x(n)+0.005.*(((y).^2)+(7*y)+2)/(3*x((y).^2)+((1-x)*(3*((y)^2)+7)));
^
you're trying to access the zeroth element of x (since y is vector with all zeroes except its first element). You need to rewrite that equation. How does the equation in your book look like?
Anyway, if you want to create a vector with 0.005 increaments use linspace or colon(:) operator.
  2 commentaires
Harry Price
Harry Price le 1 Déc 2017
This is my equation on paper.
KL
KL le 1 Déc 2017
if you have access to symbolic math toolbox, it's a lot easier. Go through the example here: https://www.mathworks.com/help/symbolic/solve-a-single-differential-equation.html#f1-7555

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