Raster calculator - negative exponential transformation gives single-value output

Question

I'm trying to apply a negative exponential transformation to a raster with values ranging from 0 to 1.

In the literature, the function to do so is R = 100 - 99 * ((1 - exp(- c * H)) / (1 - exp(-c))) where R are the resulting values, H is the original value, and C is a constant, in my case 8 (due to a c8 negative transformation). So my expression in ArcMap 10.7 is:

100 - 99 * ((1 - Exp(-8 * "LAYERTOBETRANSFORMED")) / (1 - Exp(-8)))

The output raster I receive, however, has '100' for every single value...

Is there something wrong with my expression, or perhaps with my raster?

Answer 1

Often ESRI map algebra expressions are parsed as integer so, your values would be interpreted as [0,1] and not 0-1. As such, you may want to declare your raster as float.

100 - 99 * ((1 - Exp(-8 * Float("X"))) / (1 - Exp(-8)))

You could also try including a zero decimal to each integer value in the equation eg.,

100.0 - 99.0 * ((1 - Exp(-8.0 * "X")) / (1.0 - Exp(-8.0)))