[GRASS-user] About Matrix Weights

Markus Neteler neteler at osgeo.org
Sat Nov 16 16:30:39 PST 2013

On Fri, Nov 15, 2013 at 4:08 PM, Glynn Clements
<glynn at gclements.plus.com> wrote:
> The way that weights are used depends upon the specific aggregate
> (method) being used.
> However, most of the aggregates have the property that multiplying all
> of the weights by the same factor won't change the final result (an
> exception is method=count).
> Also, most (if not all) of them have the properties that an integer
> weight of N is equivalent to N occurrences of the cell value, and
> having all weights equal to one produces the same result as when
> weights are not used.
> When weights are used, the calculation for method=average is:
>         sum(w[i]*x[i]) / sum(w[i])
> In the case where all weights are zero, this will end up with both the
> numerator and denominator to zero, which produces a null result.

I have taken liberty to merge this into the manual in r58242.

TODO: add example...


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