Calculation using exp() function in raster calculator of QGIS fails

Question

I have been trying to use this expression in the QGIS raster calculator:

1 / (1 + exp(-(β0 + β1 * RasterX1 + β2 * RasterX2 + ... + βn * RasterXn)))

The above expression has been replaced with the relevant coefficients and raster surfaces. However, the expression seems to be invalid. After testing different parts of the expression, it seems that the problematic part of the expression is the "exp", i.e. exponential.

Any solutions? Is there any variation to how the exponential is calculated using the QGIS Raster Calculator?

Answer 1

I think this can be solved with the ^ opperator. Which can be used like this:

X ^ (Y) would translate to 'X to the power of Y'.

Since the exp() function uses e as the base you can recreate exp() with 2.71828 ^(...). Hence your code can be adapted like the below example.

1 / (1 + 2.71828 ^ (-(β0 + β1 * RasterX1 + β2 * RasterX2 + ... + βn * RasterXn)))