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## fsolve not finding correct answer

**From**: |
Aivo Jürgenson |

**Subject**: |
fsolve not finding correct answer |

**Date**: |
Sun, 11 Feb 2007 22:17:47 +0200 (EET) |

Hello,

`I'm trying to use fsolve for finding unknown $k$ in a somewhat complex
``equation
`
$ p = \int_{-k}^{k} f_B(y,\sigma) dy $

`where f_B is the probability density function of "Bessel's"
``distribution and equals to
`
p=(1/(pi.*sigma)).*besselk(0,(abs(y)./sigma));
where besselk is the standard Octave function.

`The problem is that the fsolve function doesn't do a very good job and
``sometimes gives "iteration is not making good progress" and
``therefore completely wrong answer as well.
`

`The appropriate code is given in the atree_bessel_find_range.m file in the
``attachment. I'm using the 2.1.73-13 Debian package of Octave.
`

`Anybody has some hints about how to persuade fsolve giving the correct
``answer or perhaps somebody could suggest a different function for solving
``the equation in the first place?
`
Aivo Jürgenson

**
**`atree_bessel_find_range.m`

*Description:* Text document

**fsolve not finding correct answer**,
*Aivo Jürgenson* **<=**