Hey all newbie to matlab, was wondering what I can do to fix the "for loop" code I have below, I am getting the "array indices must be positive integers." Thanks in advance!

clear;

counter = 0;

for t = -15:0.2:15;

y(t) = counter;

counter = ((t^4)-(3*t^2)+(2*t)-1)

end;

Answer 1

[DGM]

Try this:

counter = 0;
t = -15:0.2:15;
y = zeros(size(t));
for k = 1:numel(t)
    y(k) = counter;
    counter = ((t(k)^4)-(3*t(k)^2)+(2*t(k))-1);
end

That said, you don't really need a loop to do this:

y2 = (t.^4 - 3*t.^2 + 2*t - 1);
y2 = [0 y2(1:end-1)];

immse(y,y2) % show that the two results are identical

Answer 2

[Kevin Holly]

clear;
counter = 0;
y=[];
for t = -15:0.2:15;
    y = [y; counter];
    counter = ((t^4)-(3*t^2)+(2*t)-1);
end

The indices for the array cannot be a negative number and has to be an integer. You cannot have an array with a value indexed at let's say 1.5.

Let's look at the first 3 values in the array

y(1:3) 

ans = 3×1

1.0e+04 * 0 4.9919 4.7291

I can view the first value as such:

y(1)

ans = 0

Let's look at the third

y(3)

ans = 4.7291e+04

I cannot view a negative nor integer