Simple Integration

Hi there,

I am new to MATLAB and have a simple question regarding the integration.

I have two expressions:

syms c L;
first = int( exp(-(L-3)^2/2, c, Inf);
second = int (first * exp(-(c-5)^2/.5), -Inf, Inf);

It gives me the integral of the first expression however on the second it says "Explicit integral could not be found". Then I also tried with quad but no avail.

what should I do to evaluate the second integral?

Many Thanks.

Answer 1

[Teja Muppirala]

QUADGK works better for integrals that go to infinity:

syms c L;
first = int( exp(-(L-3)^2/2), c, Inf);
second = matlabFunction (first * exp(-(c-5)^2/.5));
quadgk(second,-inf,inf)

[Bibha]

It worked!

Thanks! Thanks! Thanks and thanks.

Answer 2

[Ivan van der Kroon]

Bibha,

It get this answer for your third line (note also that on line two a right bracket is missing).

second =

     infinity
    /
   |                                  2
   |          exp(-2.000000000 (c - 5) )
   |
  /
    -infinity

                 1/2  1/2          1/2          1/2          1/2  1/2
        (- 1/2 pi    2    erf(1/2 2    c - 3/2 2   ) + 1/2 pi    2   ) dc

I really do not think this integral can be evaluated explicitly. It is an error-function multiplied with a exponential function.

Ciao, Ivan

[Bibha]

I think, I agree with you that the integral can NOT be evaluated explicitly. For that reason, I tried QUAD but I could not get it worked.

Any help on QUAD?