MATLAB: Integration problem, getting wrong answer in matlab

exponentialintegral

Good morning I have an integration that I need to compute, I used MATLAB but I did not get the right answer.

This is the integral:

   exp(-(t-1)^2/(σ^2)) dt

from -Inf to Inf. I am getting that it equals zero which is impossible, can any one help me?

Thank you in advance

Best Answer

How are you doing the integration?

>> sigma = 7
sigma =
     7
>> syms t
>> exp(-(t-1)^2/(sigma^2))
ans =
exp(-(t - 1)^2/49)
>> int(ans,t,-inf,inf)
ans =
7*pi^(1/2)

Related Solutions

MATLAB: Improper integral

I don't think quad ever allowed infinite limits. quadgk does. The answer you need depends on how old your MATLAB version is. I am going to express an answer in more recent syntax. If you try

a=0; b=1; 
fun = @(u) exp(-a.* exp(2.*u)).*exp(-(u + b.^2).^2./2.*b.^2)/...
  (sqrt(2.*pi.*b.^2));
quad(fun,-Inf,Inf)

then you get this message:

Warning: Infinite or Not-a-Number function value encountered.

and the answer is NaN. The likely reason is that there is underflow in these exponential expressions:

>> fun(1000)
ans =
   NaN

However, if you plot this function, you can see that this function approaches zero very rapidly. For example,

>> fun(0)
ans = 
    0

Therefore, you can do this calculation:

quadl(fun,-100,100)
ans = 
    1.0000

This is 1 to an accuracy of about 10^-8.

Note: the fun = ... line is an anonymous function.

MATLAB: Which packages do I need to use ‘integral’ function

use function quadgk

>> fun = @(x) exp(-x.^2).*log(x).^2;
>> quadgk(fun,0,inf)
ans =
       1.9475

Best Answer

Related Solutions

MATLAB: Improper integral

MATLAB: Which packages do I need to use ‘integral’ function

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