differentiation with respect to space

Hello I am doing differentiation with respect to space. I have a function y which is x^2. x is my coordinate. I want to differentiate y with respect to x and I use 'diff' function. I know dy/dx=2*x. so I compare my result of differentiating (in fig3) with the plot of y=2*x (fig.2) and they are not the same. And also how can I have the same length after differentiating? Any help is appreciated. friet.

clear all clc

x=linspace(-1,1,100);
y=x.^2;

figure(1)
plot(x,y)

z=2.*x;
figure(2)
plot(x,z)

u=diff(y,x);

figure(3)
plot(x(1:99),u)

Answer 1

[Star Strider]

Since you are doing numeric, rather than symbolic, differentiation, use the gradient (link) function, not diff.