Integration of lnx*exp(x)

  • #1
Integration of following (limit -∞ to +∞):

1/√(2πσ^2) ∫ln(x) * exp{-(x-μ)^2 / (2σ^2)} dx

After one-step (integration by parts) it looks like the following:
lnx + ∫ σ/(√2π) * exp[{-(x-μ)^2 / (2σ^2)} / {x (x-μ)}] dx

After another-step (by parts), it looks like the following:
lnx + ∫ 1/(√2πσ^2) * exp[{-(x-μ)^2 / (2σ^2)} / {x^2}] dx

I don't think I am doing it right. Could anybody please throw some lights or may be alternative ways to achieve it?
 

Answers and Replies

  • #2
Ray Vickson
Science Advisor
Homework Helper
Dearly Missed
10,706
1,728
Integration of following (limit -∞ to +∞):

1/√(2πσ^2) ∫ln(x) * exp{-(x-μ)^2 / (2σ^2)} dx

After one-step (integration by parts) it looks like the following:
lnx + ∫ σ/(√2π) * exp[{-(x-μ)^2 / (2σ^2)} / {x (x-μ)}] dx

After another-step (by parts), it looks like the following:
lnx + ∫ 1/(√2πσ^2) * exp[{-(x-μ)^2 / (2σ^2)} / {x^2}] dx

I don't think I am doing it right. Could anybody please throw some lights or may be alternative ways to achieve it?
The question does not make sense: ln(x) is not defined for x < 0 (or, at least, is not unique). Are you sure the integration does not go from x = 0 to +∞?

RGV
 

Related Threads on Integration of lnx*exp(x)

  • Last Post
Replies
2
Views
5K
  • Last Post
Replies
2
Views
1K
Replies
6
Views
10K
  • Last Post
Replies
10
Views
11K
  • Last Post
Replies
5
Views
6K
Replies
1
Views
835
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
4
Views
5K
  • Last Post
Replies
4
Views
1K
Replies
11
Views
3K
Top