Getting 0 when using quad

 fun = @(x) 80*exp(-((x-pi)/0.002).^2);
 I = quad(fun,0,6)

 I2= integral(fun,0,6)

I =

     0

I2 =

     1.464129900321425e-69

Why do I get 0 when using quad?

Best regards Aldo

Answer 1

[Walter Roberson]

The two use different adaptive techniques. The function has a sharp peak at Pi and one technique misses it completely and the other barely catches it. The actual integral over that range is (2/25*(erf(500*Pi)+erf(3000-500*Pi)))*sqrt(Pi) which is about 0.284

To get a better answer:

integral(fun,0,6,'Waypoints', pi)

[Aldo]

And how should you go about to solve it with Quad?

[Walter Roberson]

I wouldn't solve it with quad(). I might solve it with quadgk

quadgk(fun,0,6, 'waypoints', pi)

Answer 2

[KSSV]

You are trying to calculate the area under the curve as shown in the attached image. See the values on the axes, so I think getting zero is legitimate.