slatec bessel_k(n, %i*x): lack of precision for large x

If you want a bfloat bessel function, I can give you one for J,
positive real order and  positive real argument.  Written in lisp for 
Maxima,
or the Maxima language.
J[n,%i*x]  =  (%i*^n) *I[n,x], so maybe all you need is a routine for I_n.

RJF


  On 3/2/2012 2:31 PM, Raymond Toy wrote:
>
>
> On Fri, Mar 2, 2012 at 11:47 AM, Edwin Woollett <woollett at charter.net 
> <mailto:woollett at charter.net>> wrote:
>
>
>     /* this calculation also agrees with Mma, but the zbesk
>      error messages clutter up the output, and
>      show why it is desireable to have a way to
>      surpress the printing of these messages to
>      the screen! */
>
>
> What would you want?  No messages so you have no way of knowing that 
> something potentially bad happened?  Signal an (annoying?) error?
>
>
>     -----------------------------------
>     The bottom line here is: are there better bessel function
>     routines available which are reasonably accurate for large
>     abs(z) args??
>
>
> Don't know.  Maybe you can compute using bfloats and return a float at 
> the end? (But we don't have a real bfloat implementation of Bessel 
> functions, so you will have to use Barton's hypergeometric code to 
> compute the Bessel functions.)
>
> Maybe bessel_k(v,%i*x) can be computed via 
> http://www.wolframalpha.com/input/?i=BesselK[v%2Cix].  (See alternate 
> form).  The Bessel J and Y functions don't appear to have problems 
> with the size of x in your tests.  But I have no idea how accurate the 
> result would be.
>
> Ray
>
>
>
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