Loop insider a loop Plot, Please Help

I need to plot a t vs. s diagram. The function is: s = (sigma - 3 + 0.072 * t * (1 + 0.072 * t)) / 0.77. I'm dying to know why the loop inside loop does not give me the correct plot. Thank you so much.

INCORRECT:

clear all;
Sigma = 0:5:30;
T = 0:1:30;
for sigma = 1:length(Sigma);
  for t = 1:length(T);
        s(sigma,t) = (sigma-3+0.072*t*(1+0.072*t))/0.77;
  end;
end;
plot(s,T)

CORRECT:

clear all;
Sigma = 5:5:30;
T = 0:1:30;
  for t = 1:length(T);
      s(Sigma,t) = (Sigma-3+0.072*t*(1+0.072*t))/0.77;
  end;
plot(s,T);

Thank you.*

Answer 1

[Walter Roberson]

In your first version, you have

 for sigma = 1 : length(Sigma)

which makes sigma 1, 2, 3, ... up to the number of values in Sigma.

In your second version, you use Sigma in your calculation, which uses the contents of Sigma rather than the numbers up to the length of Sigma.

Fix:

s(sigma,t) = (Sigma(sigma)-3+0.072*t*(1+0.072*t))/0.77;

Answer 2

[Azzi Abdelmalek]

clear 
Sigma = 5:5:30;
n=numel(Sigma)
t = linspace(0,30,n);
s=zeros(1,n);
for k = 1:n;
  s(k) = (Sigma(k)-3+0.072*t(k)*(1+0.072*t(k)))/0.77;
end;
plot(t,s);

[Michael Wolf]

Thank you guys so much. I figured it out