## FNbessI0

#### Routine

double FNbessI0 (double x)

#### Purpose

Evaluate the zeroth-order modified Bessel function of first kind

#### Description

This function returns the value of the zero'th order modified Bessel function of the first kind. This function is defined as

                1   2 pi
      I0(z) = ----  Int exp (z cos(a)) da.
              2 pi   0

This routine calculates an approximation using an infinite series. This series is rapidly converging for moderate values of z.

#### Parameters

<- double FNbessI0
  Returned value
-> double x
  Input value

#### Author / revision

P. Kabal / Revision 1.3 2003/05/09

Main Index libtsp