[GRASS-dev] r.mapcalc addition

[Glynn Clements]

Joel Pitt wrote:

> It'd be great if someone could commit the attached addition to r.mapcalc
> 
> It basically allows one to specify the seed for random number
> generation by adding a new function "erand(a,b,s)" which takes a and b
> as the lower and upper limit, and s is a seed that is used to initiate
> the pseudo random number generator.
> 
> This is useful in modelling and simulation so that particular
> replicates can be rerun exactly.
> 
> If it needs any extra work let me know and I'll make the changes.

I consider this to be the wrong approach. At a minimum, setting the
seed should be decoupled from the generation of random numbers;
there's no reason to have what is essentially another copy of
f_rand().

Also, it's debatable whether an r.mapcalc function is the correct
mechanism for setting an operating parameter. An environment variable
might be more suitable.

Finally, even if f_erand() was the correct interface, having it call
f_rand() once the seed has been set is preferable to including a clone
of f_rand() in the body of f_erand().

-- 
Glynn Clements <glynn at gclements.plus.com>