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?