[GRASS-dev] Re: [GRASS-user] Re: Calculating standard error of many maps?

[Hamish]

Glynn Clements wrote:
> I can add sum of squares/cubes/etc to r.series easily
> enough if there is a use for them.

well, sum of squares is useful so you can calculate variance & friends.
don't know of any use for cubes+.

r.univar/stats.c:
    /* all these calculations get promoted to doubles, so any DIV0 becomes nan */
    mean = stats->sum / stats->n;
    variance = (stats->sumsq - stats->sum * stats->sum / stats->n) / stats->n;
    if (variance < GRASS_EPSILON)
        variance = 0.0;
    stdev = sqrt(variance);
    var_coef = (stdev / mean) * 100.;   /* perhaps stdev/fabs(mean) ? */


adding sum of sq would let people calc that with r.series+r.mapcalc
manually.

not sure what components are required to calc kurtosis & skewness,
although I've an idea that they'd be possible with a single-serial-pass
construction method as s.cellstats had them (??).

perhaps 'mean of absolute values' too?


Hamish