Re: defined

[Ethan A M. <merritt@u.washington.edu>]

On Monday 29 May 2006 03:28 pm, Daniel J Sebald wrote:
> This seems like a bug, even though the syntax is incorrect... but a user might think the syntax is correct if gnuplot doesn't complain but rather returns a non-zero value that will always test positive.
> 
> gnuplot> print defined("foo")
> 141158968

We don't have a user-visible TBOOLEAN type, 
so any non-zero value represents "TRUE"
 
> Also, would it be useful to extend defined() from just variables to functions as well?  
> Say, return 1 if user defined variable, 2 if internal variable, 3 if user defined function, 
> 4 if internal function.  

What would you do with this information?

> That way, the defined() function could be used inside stat.inc as
> 
> if (defined(gamma)!=3) gamma(x) = exp(lgamma_nat(x))

But that will always be true.
The conditional compilation is set during configuration so that you
always get a gamma function.  The only question is whether you get
one from a system library or whether you get one from gnuplot's 
inline code.

> then get rid of these comments like:
> 
> # If you have the lgamma() function compiled into gnuplot

> As soon as someone starts uncommenting/commenting code it becomes confusing.

That comment is confusing to me already.  My reading of the
code leads me to believe that gnuplot will always provide a
lgamma() function.  Again there is a question of whether this
came from a system library or not.  But either way you can
use the function.





> , you can use 
> # alternate definitions for some PDFs. For larger arguments this will result
> # in more efficient evalution. Just uncomment the definitions containing the
> # string `lgamma', while at the same time commenting out the originals.
> # NOTE: In these cases the recursive definition for lgamma() is NOT sufficient!
> 
> 
> 
> Last, how about an internally defined 'eps' or something similar to represent float machine precision?
> 
> 
> Oh, one other thing.  Any interest in a complex version of the gamma function?
> 

-- 
Ethan A Merritt
Biomolecular Structure Center
University of Washington, Seattle 98195-7742