# Getting range value from exponential variogram model

I am using `vgm()` from the `gstat` library in R:

``````variogr <-vgm(sill,"Exp",range=range,nugget=0)
output <-krige(...,model=variogr)
``````

As you can see I'm using fixed psill and range values.

Before this, another script (on which I have not control) is evaluating the variogram parameters. Namely, I know that my points fit well in a `p1*(1-exp(-x/p2))`, and I am given the exact values of `p1` and `p2`. My question is how to get sill and range (`sill` and `range`) from the exponential model parameters `p1` and `p2`?

I know that the sill value is `== p1`, because we are choosing nugget to be zero. But I'm having troubles finding which value should I give to the range. I have been told by my professor that `range == p2`, but from what I have read elsewhere there should also be a factor (like, `p2 == k*range`) that might have different values depending on the proper definition of range.

So, given `p1` and `p2`, which value should I use as a `range` input to the `vgm()` function? Is it true that `range == p2`? What kind of range is vgm() expecting me to put in?

Yes, this is true. Your professor is right. Look for function `fn_exponential` in the source code if you want to be sure.