f(x) =


     a*exp(-(b/x)^n)+c


a: the long-range value of f(x), set range from 0 to 20, step .5
b: the healing distance, set range from 0 to 20, step .5
n: a measure of how fast the function "heals",set range from 0 to 12, step 1
c: the base value of f(x)