How to get defined integral?

Hi, I have a small project due in a couple of hours. Currently I'm using the following code:

x = linspace(-3,6,1000); % Define x-interval as -3 to 6 with 1000 points defined in vector

y = x.^3 - 5*x.^2 - 4*x + 20; % Define y as equation

plot(x,y)

Now I have to find the defined integral over the interval -2,5. A minute ago I put the following into the command window:

int(x.^3 - 5*x.^2 - 4*x + 20,-2,5)

and got the right answer. But now suddenly it doesn't work. I get the error:

Undefined function 'int' for input arguments of type 'double'.

What's the problem here? Also, once it works, how do I get an output when written in the editor and run (will it show a window like the axes plotted or do I have to tell it to show the output somewhere?)

Thanks

Answer 1

[Andrei Bobrov]

x = linspace(-3,6,1000);
y = x.^3 - 5*x.^2 - 4*x + 20; 

out = quad(@(x)x.^3 - 5*x.^2 - 4*x + 20,-2,5);

or

out2 = diff(polyval(polyint([1 -5 -4 20]),[-2,5]));

or your case

syms x
out3 = int(x.^3 - 5*x.^2 - 4*x + 20,-2,5)

or if you use MATLAB R2012a or R2012b

out4 = integral(@(x)x.^3 - 5*x.^2 - 4*x + 20,-2,5);

Answer 2

[Walter Roberson]

The "int" call would have worked if you had used

 syms x

before you made the int() call, and you had not assigned any numeric value to x between the "syms" command and the int() call.