First off, I know I can use the trapz or quad functions on matlab, but I want to derive my own numerical integration code. The problem is more complicated than this, but basically I need to be able to numerically integrate in matlab to continue with the homework assignment. If y = x^2 is the function of interest to be numerically integrated from 0 to 4, this is what I have so far: x_step = 0.1; x = 0:x_step:4; y = x.^2; y2 = (x.^3)/3; N = length(y) for i=1:N-1 int_y(i) = ((y(i)+y(i+1))./2)*x_step %employing trapezoidal rule end plot(x,y), hold on, plot(x(1:N-1),y_int,'r'), hold on, plot(x,y2,'g') %just to see if i'm right It doesn't work. Any suggestions? Can anyone link me to the code for the trapz function for matlab? I looked for a little bit, but couldn't find it. I'm not sure if we can just use trapz, so just to be safe, I wanted to develop the code myself. I can take a numerical derivative pretty easily with matlab, so I don't understand why this won't work for me! Thanks for any help.