Problem with derivative function syntax

Ok so basically what I'm doing here is trying to graph a function and its derivative in matlab. This is what I have:

clear; clc; close all; x=(-2:0.1:4); y=x.^3-2*x.^2-10*sind(x).^2-exp(0.9*x); yd=3*x.^2-4*x-20*sind(x)*cosd(x)-0.9*exp(0.9*x); plot(x,y,x,yd,'--'); xlabel('X Values'); ylabel('Y Values'); legend('function', 'first derivative')

There are no errors in my original function. But for some reason, the derivative function keeps giving me an error. It says "Error using * Inner matrix dimensions must agree. If anyone can help me fix the syntax, it would be greatly appreciated!

Answer 1

[Star Strider]

Since sind and cosd are both functions of row vector ‘x’, they produce row vectors as output. To multiply them, you need to vectorise them, replacing (*) with (.*):

yd=3*x.^2-4*x-20*sind(x).*cosd(x)-0.9*exp(0.9*x);

With that change, it works!