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Besseli Function

From: John W. Eaton
Subject: Besseli Function
Date: Mon, 8 Sep 2003 11:33:19 -0500

On  8-Sep-2003, Jose Otavio Bueno <address@hidden> wrote:

| I'm having problems with the Besseli Functions in Octave. While with 
| Mathlab it is possible to solve the besseli functions with values up to 
| 700, with Octave the function returns a valid answer just for input 
| values below 81:

Octave allows you to ask to have the result from besseli scaled by
exp(-abs(x)).  So you can write

  exp (abs (x)) * besseli (0, x, true);

(the last argument to besseli can be anything, its presence just means
"scale the result").  By doing this, Octave returns

  octave:1> x = [1,10,81,82,700];
  octave:2> exp(x).*besseli (0, x, true)
  ans =

      1.2661e+00    2.8157e+03    6.6864e+33    1.8064e+34   1.5296e+302

It might be useful if Octave detected the overflow (the internal
function zbesi provides that information) and then attempted to
perform the scaled calculation instead.  Can someone please look at
providing a patch for that?

Also, the documentation for the scaling option could be better, so a
patch for that would also be appreciated.



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