Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Integral of tan(logx)

  1. Jun 21, 2009 #1
    What is integral of tan(logx)? I couldn't find it on internet.
     
  2. jcsd
  3. Jun 21, 2009 #2

    CompuChip

    User Avatar
    Science Advisor
    Homework Helper

    It doesn't seem to be expressible in elementary functions, at best you will get Euler Beta functions.
     
  4. Jun 21, 2009 #3
    Last edited by a moderator: Apr 24, 2017
  5. Jun 21, 2009 #4
    Were you just wondering, or do you need to find it for an assignment? Because you should be aware that if you just come up with an integral with elementary functions, there's a good chance that it won't be expressible in terms of elementary functions.
     
  6. Jun 25, 2009 #5
    Maple does it in terms of the Lerch [tex]\Phi[/tex] function.
     
  7. Jun 28, 2009 #6
    Mathematica:

    [itex]-i \left(\left(\frac{1}{5}-\frac{2 i}{5}\right) x^{1+2 i} \text{Hypergeometric2F1}\left[1-\frac{i}{2},1,2-\frac{i}{2},-x^{2 i}\right]-x \text{Hypergeometric2F1}\left[-\frac{i}{2},1,1-\frac{i}{2},-x^{2 i}\right]\right)[/itex]
     
  8. Jun 28, 2009 #7
    A wonderful case of the mathematics required to understand the problem far-exceeding that required to solve it O_O.
     
  9. Jun 29, 2009 #8

    CompuChip

    User Avatar
    Science Advisor
    Homework Helper

    You might want to use FullSimplify (possibly with the additional assumption that x is real) and arrive at something with Euler B's, as I said.
     
  10. Jun 29, 2009 #9
    [itex]\text{FullSimplify}[\text{Assuming}[x\in \text{Reals},\int \text{Tan}[\text{Log}[x]] \, dx]][/itex]

    [itex]
    i x \text{Hypergeometric2F1}\left[-\frac{i}{2},1,1-\frac{i}{2},-x^{2 i}\right]-\left(\frac{2}{5}+\frac{i}{5}\right) x^{1+2 i} \text{Hypergeometric2F1}\left[1,1-\frac{i}{2},2-\frac{i}{2},-x^{2 i}\right]
    [/itex]

    I'm just copying what it says. I have no idea about all the non elementary functions that pop out or how to see them without resorting to mathematica. e.g. integrating gaussian distribution thing. A source for this information would be good.
     
  11. Jun 30, 2009 #10

    CompuChip

    User Avatar
    Science Advisor
    Homework Helper

    You might want to simplify with the assumption that x is real:

    [tex]\text{Assuming}[x \in \text{Reals}, \text{FullSimplify}[\int \tan[\log[x]], x]][/tex]

    gives
    [tex]
    \frac{1}{2} \left(-x^{2 i}\right)^{\frac{i}{2}} x \left(B_{-x^{2
    i}}\left(-\frac{i}{2},0\right)+B_{-x^{2
    i}}\left(1-\frac{i}{2},0\right)\right)
    [/tex]

    which for evaluation purposes doesn't help you, it's just prettier (or less ugly, if you like) to look at.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Integral of tan(logx)
  1. Integrating tan(x) (Replies: 2)

  2. Integral of sqrt(tan x) (Replies: 10)

Loading...