MATLAB: Euler Method array problem ‘Unable to perform assignment because the left and right sides have a different number of elements.’

Question

Hello everyone.

I'm new to matlab and tried to create euler method code on my own.

function [t,y] = eulerian13th(t0,y0,n,b,a)
t= t0
for i = 1:n
    f = (-t)*y0
    h = (b - a)/n
    t(i+1) = h + t0 
    y(i+1) = y0 + h*f
    t0 = t(i+1);
    y0 = y(i+1);
    hold on;
    plot(t,y);
    grid on;
    chuzkun = [t;y];
    fprintf('%6s %12s\n','t','y');
    fprintf('%6.f %12.f\n',chuzkun);
    end
end
    

This is the line of my code that i have a problem with

y(i+1) = y0 + h*f

I know what my problem is coming from the function itself, because it has (-t) and y0, when it only has y0, the error didn't appear.

f = (-t)*y0

i have done read some forum regarding this problem, its because array and cell probem, but i still cant find the solution.

Hopefully i can get the answer and sugestion from you all.

Thank you very much.

Answer 1

't' is a vector, Change the line

f = (-t)*y0

to

f = (-t0)*y0

Also, plotting inside for loop like your code is very efficient and you will find that your code will run very slow. The proper way is like this

function [t,y] = eulerian13th(t0,y0,n,b,a)
t= t0
f = figure();
ax = axes();
hold(ax);
grid on
l = line(nan, nan);
for i = 1:n
    f = (-t0)*y0
    h = (b - a)/n
    t(i+1) = h + t0 
    y(i+1) = y0 + h*f
    t0 = t(i+1);
    y0 = y(i+1);
    l.XData(end+1) = t0;
    l.YData(end+1) = y0;
    chuzkun = [t;y];
    fprintf('%6s %12s\n','t','y');
    fprintf('%6.f %12.f\n',chuzkun);
    end
end