[GRASS-dev] using rand(x,y) in r.mapcalc (grass7)

Vaclav Petras wenzeslaus at gmail.com
Tue Jul 22 19:13:50 PDT 2014

On Tue, Jul 22, 2014 at 8:14 PM, Glynn Clements <glynn at gclements.plus.com>

> r61353 changes r.mapcalc so that seeding is performed via seed= or -s.
> The seed (whether specified by seed= or generated for -s) is added to
> the history (for r.mapcalc; r3.mapcalc's create_history() function is
> a stub; do 3D rasters have history?)

I added test for r61353 in r61355. Tests are only for r.mapcalc not for


> As I write this, it has occurred to me that the behaviour of rand()
> may be non-deterministic in the presence of certain forms of
> parallelism, e.g. multiple occurences of rand() in the expression(s)
> in conjunction with pthreads. Ultimately we may need to expand the
> PRNG to support explicit state (as per erand48, nrand48 and jrand48).

The tests are not testing any of this (at least not explicitly),
contributions welcome.
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