[GRASS-user] geometric mean with r.mapcalc
Hamish
hamish_b at yahoo.com
Tue Jun 17 08:50:32 EDT 2008
Valentina wrote:
> I tried to calculate the geometric mean with float numbers
> for six raster maps, but the result was a map with only one
> value: 1.0.
> I used the formula: (A*B*C*D*E*F) ^ (1/6), and also:
> pow((A*B*C*D*E*F), (1/6)) but I get always the same result: 1.0.
> Could somebody help me?
try: pow((A*B*C*D*E*F), (1/6.0))
The result of an integer/integer calculation is an integer, so 0.166667 is truncated to 0 and the result will be x^0, which is always equal to 1.
In this manner r.mapcalc just follows what the C programming language does, the quirk is not really specific to r.mapcalc or GRASS.
Hamish
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