# Evaluating the area between two curves.

176 views (last 30 days)
Ejay Kasai on 12 Sep 2011
how to Evaluate the area between two curves using matlab? for example this one y=x^2 and y=2*x

Grzegorz Knor on 12 Sep 2011
syms x
x0 = eval(solve('x^2 -2*x'));
x = linspace(x0(1),x0(2),100);
y1 = x.^2;
y2 = 2*x;
fill([x x(end:-1:1)],[y1 y2(end:-1:1)],'r')
hold on
plot(x,y1,x,y2,'LineWidth',2)
grid on
a = trapz(x,y2)-trapz(x,y1);
syms x
x0 = eval(solve('x^2 -2*x'));
You can use:
x0(1) = fzero('x.^2 -2*x',1);
x0(2) = fzero('x.^2 -2*x',1.5);

Oleg Komarov on 12 Sep 2011
Grzegorz has given you a valid solution. If you really needed the value you wouldn't have posted the comment in the first place since it's in the code.
Ejay Kasai on 13 Sep 2011
i mean i need a code to evaluate the area between the two curves. i need to make a matlab program for that.
Walter Roberson on 13 Sep 2011
The expression Grzegorz gave, a = trapz(x,y2)-trapz(x,y1) *is* the code to evaluate the area between the two curves. This is elementary calculus: the area between two curves is the difference between their integrals. trapz() calculates numeric integrals.