nexp

This function is the sum of decaying exponentials. It has the form:

f (x) = $\displaystyle \sum$Θ(ai)ai+2e$\scriptstyle {\frac{{x-a_i}}{{a_{i+1}}}}$ + an-1,

where Θ(ai) = 0 if x < a, and Θ(ai) = 1 if x≥a. You need to tell the program how many parameters you want. 4 parameters gives you one exponential, 7 gives you two, etc. If you know the offset, you should initialize properly and not vary that parameter. For example, most decaying exponentials are triggered by some event. If you know the time of the event, don't vary that parameter.