Hi Mikael,
Thank you, as ell as Alan and Henri, for giving us a simple way to use Bessel
functions, directly in ConTeXt.
However I have a question, which may show my total ignorance of the maths
libraries ffi and consorts: how do you specify the value of the integr $n$ when
you want to use $J_{n}(x)$?
Best regards: OK
> On 12 Dec 2018, at 21:13, Mikael P. Sundqvist <mic...@gmail.com> wrote:
>
> On Wed, Dec 12, 2018 at 9:02 PM Henri Menke <henrime...@gmail.com> wrote:
>>
>> On 13/12/18 8:56 AM, Alan Braslau wrote:
>>> On Wed, 12 Dec 2018 20:42:56 +0100
>>> "Mikael P. Sundqvist" <mic...@gmail.com> wrote:
>>>>
>>>> Thanks, Alan! That looks very promising. I could not make it work,
>>>> though, and I guess that is because I use linux and do not know what
>>>> to change for what. I installed libcerf but I assume something else is
>>>> missing. In any case, this is one of the things it would be nice to
>>>> have, at least as a module. I have no idea on how to realize that,
>>>> though.
>>>>
>>>> /Mikael
>>>
>>> You likely also need to install libffi - I do not know what package
>>> this is on your flavor of linux - Luigi is the ffi specialist!
>>
>> FFI is integrated in LuaTeX >= 1.03
>>
>> In you example you load libcerf but you are not using it. What you are
>> actually using are the Bessel function from the C Standard library. GCC
>> includes them as a GNU extension.
>> https://www.gnu.org/software/libc/manual/html_node/Special-Functions.html#index-j0
>> Your example also works if you remove libcerf (at least for me on Linux).
>>
>
> Thanks Henri! Indeed it worked now. The following example (just in
> case someone else did not get what to change) compiles here, and shows
> the expected graph. This is very good news!
>
> \startluacode
>
> ffi = require("ffi")
> ffi.cdef[[
> double j0(double x);
> double j1(double x);
> double jn(double x);
> ]]
>
> \stopluacode
>
> \startMPdefinitions{doublefun}
> vardef jzero primary x = scantokens(lua("mp.quoted( ffi.C.j0(" &
> decimal x & "))")) enddef ;
> vardef jone primary x = scantokens(lua("mp.quoted( ffi.C.j1(" &
> decimal x & "))")) enddef ;
> vardef jn primary x = scantokens(lua("mp.quoted( ffi.C.jn(" &
> decimal x & "))")) enddef ;
> \stopMPdefinitions
>
>
> \starttext
> \startMPpage[instance=doublefun]
> draw function(1,"x","jone(x)",epsed(0),epsed(10),1/10) scaled 1cm;
> \stopMPpage
> \stoptext
>
> /Mikael
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