How to write Bessel function

Hi there, I’m trying to write a Bessel function in Grasshopper.
I already found this post, but unfortunately the link to the dll and this site are not available at the moment. Maybe somebody knows a way to do it?

moved to Grasshopper category

Same thing for me. Anyone who still has the VB script linked in the post above?

Hoping for you @laurent_delrieu :pray:

You can try mpmath

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Thank you.

I’ve tried to find info on how to make mppath available to Grasshopper. How is it done?

I’ve downloaded the release from their website, but don’t know what to do with the files

Much appreciate your assistance.

Download the library from this link

and extract to:
C:\Program Files\Rhino 7\Plug-ins\IronPython\Lib

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Thanks a lot.

I suppose there is no way to make these sources available to grasshopper from a folder that isn’t within administrator rights? We’re a bigger office and I can’t just copy things to system folders sadly.

Check the first method to let Rhino use some Python27 modules, than you can install mpmath directly to Python27 and use it

So our system admin was kind enough to copy the mpmath folder into C:\Program Files\Rhino 7\Plug-ins\IronPython\Lib for me.

But after restarting Rhino and GH:

I worry Python itself must also be installed…? Python Releases for Windows |

I found solution how to install here
It works for me)

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Check the folders in Python options


I’ve added that search path, thanks to the explanation posted by @alenustins.

It still won’t work :cry:
Grasshopper cannot find the module.

@alenustins is it mandatory that mppath be saved under site-packages\ ?

I don’t know your level in mathematics, but making an integral is not so difficult. It is 5 lines of code.
Here an approximation using Wikipedia equation and Euler integration

  private void RunScript(double x, int n, ref object A)
    //Laurent Delrieu

    double j = 0;
    double dteta = 0.001;
    for (double teta = 0; teta <= Math.PI; teta += dteta)
      j += Math.Cos(n * teta - x * Math.Sin(teta));
    j = dteta * j / Math.PI;
    A = j;

    Component.Message = "Bessel Function";

Bessel Function (9.7 KB)

Error is :sweat_smile: 0.001 with dteta = 0.001
2 10e-6 with dteta = 0.0001 (n=0 and 2)
30 10e-6 with dteta = 0.0001 and n=1


Well my level of mathematics is certainly not yours :sweat_smile:

This is amazing, thank you !!

Note that it works only for integer and it is not optimized so it is far less fast that using a dedicated library.
Here the old library (109.4 KB)

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