Re: question about the inverse li function

*To*: mathgroup at smc.vnet.net*Subject*: [mg65383] Re: question about the inverse li function*From*: Bill Rowe <readnewsciv at earthlink.net>*Date*: Wed, 29 Mar 2006 06:34:25 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

On 3/28/06 at 4:05 AM, Arthur.Capet at student.ulg.ac.be (Capet Arthur) wrote: >the question... >i've measured C(x), wich is equal to li(I(x)), where li denotes the >logarithmic integral function. I would like to compute I(x)= >li^(-1) (C(x)) >how can i compute the inverse of the logarithmic integral function >? Is there a function Inverse[_function] ? Yes, there is a function for computing inverses of functions, InverseFunction. But, function will only provide and inverse function where there is a defined inverse function. That is, InverseFunction[Sin] gives ArcSin but InverseFunction[LogIntegral] won't give you something useful. One way to solve the problem would be to use FindRoot, i.e. In[10]:= FindRoot[LogIntegral[x] == -1, {x, 1.1}] Out[10]= {x -> 1.1882560662743253} or if you wanted the other root In[16]:= FindRoot[LogIntegral[x] == -1, {x, 0.9}] Out[16]= {x -> 0.7674077436558667} -- To reply via email subtract one hundred and four