Euler function where you can define equation, starting x and y values, number of steps and the step length

This is what I have thus far
function [xverd, tilnaer] = Euler_met (f,x0,y0,no_steg,lengde)
g = @(x,y) f;
t = x0:0.01:x0+no_steg;
y = zeros(1,length(t));
y(1) = y0;
fprintf('\n x        y ')
for s = 1:length(t)-1
    fprintf('\n%4.3f  %4.3f ',t,y)
    y(s+1) = y(s)+lengde*g(t(s),y(s));
end
plot(t,y)
end

But when I try to run it with these values:

Euler_met(8*cos(x+y),0,4,10,0.01)

I get this error:

Undefined operator '*' for input arguments of type 'function_handle'.

Error in Untitled>Euler_met (line 10)

y(s+1) = y(s)+lengde*g(t(s),y(s));

I've tried just defining the equation f in line 3 in the code as such:

g = @(x,y) 8*cos(x+y);

And that works perfectly, so why can I replace the equation as seen in the code at the top?

Answer 1

[Torsten]

Use g = f or g = @(x,y) f(x,y) instead of g = @(x,y) f.

[Heine Rugland]

for g = @(x,y) f(x,y) I get:

Index in position 1 is invalid. Array indices must be positive integers or logical values.

Error in heineruglandinnlevering3>@(x,y)f(x,y) (line 55)

g = @(x,y) f(x,y);

Error in heineruglandinnlevering3>Euler_met (line 62)

y(s+1) = y(s)+dt*g(t(s),y(s));

For g = f I get:

Index in position 1 is invalid. Array indices must be positive integers or logical values.

Error in heineruglandinnlevering3>Euler_met (line 62)

y(s+1) = y(s)+dt*g(t(s),y(s));

[Torsten]

Of course, f should already be a function handle

Euler_met(@(x,y)8*cos ...,0,4,10.0.1)

[Heine Rugland]

Thank you so much!