index exceeds matrix demension

figure(1)
hold on;
plot(1.25,1.25,'ro');
i=1;
while i <= 20
    plot([xi(i),xj(i)],[yi(i),yj(i)],'b');

      i= i+1
  end
  title('graph')
  grid;
  box;
  ax = gca;
  ax.YAxisLocation = 'origin';

keep on getting index exceeds matrix demension... could you please help??

[Jan]

Please post the complete error message. Then the readers do not have to guess, where the error occurs. Without your input data, we cannot guess, which variable is affected. But it could even be a redefining of "title" as a variable.

[Walter Roberson]

Note that when i becomes 2, then xi(i) will not refer to a variable named x2: it will continue to refer to a variable xi

Answer 1

[Image Analyst]

Your 4 vectors have a length less than 20. Before the loop put this, and you'll see (in the command window)

size(xi)
size(xj)
size(yi)
size(yj)

Do they all go up to 20? No, evidently not or you wouldn't be getting an error message. If you still need help, attach your xi, xj, yi, and yj.