s19adf

Purpose

Synopsis

[fun_value,ifail] = s19adf(x<,ifail>)

Description

 
 This routine evaluates an approximation to the Kelvin function 
 kei x.
 
 Note: for x<0 the function is undefined, so we need only consider
 x>=0.
 
 For x<0, the function is undefined, and hence the routine fails 
 and returns zero.
 
                                                   _____      _    
                                                  / (pi) -x/\/2    
 For large x, kei x is asymptotically given by   /  ----e       
                                               \/    2x           
                                                                 
 and this becomes so small that it cannot be computed without 
 underflow and the routine fails.
 

Parameters

s19adf

Required Input Arguments:

x                                     real

Optional Input Arguments:                       <Default>

ifail                                 integer  -1

Output Arguments:

ifail                                 integer