[julia-users] Re: exponential integral

[Steven G. Johnson]

On Monday, June 2, 2014 2:19:00 PM UTC-4, anonymousnoobie wrote:
>
> Does julia have a package or library to compute exponential integral 
>
>   http://en.wikipedia.org/wiki/Exponential_integral 
> <http://en.wikipedia.org/wiki/Exponential_integral> 
>
> for real positive argument  arbitrary precision ??
>

Yes, the exponential integral function is included with the MPFR library, 
which is bundled with Julia and used for its BigFloat (arbitrary precision) 
type.

However, currently it's not exposed by a nice API, so you have to define:

function eint(x::BigFloat)
    z = BigFloat()
    ccall((:mpfr_eint, :libmpfr), Int32, (Ptr{BigFloat}, Ptr{BigFloat}, 
Int32), &z, &x, Base.MPFR.ROUNDING_MODE[end])
    return z
end

and then you can do e.g. 

eint(big(2.2))

to compute Ei(2.2) in arbitrary precision.