Werner,
Sorry for the bad explanation. I did try various polynomial curve fit with various degrees 6 through 10 but with no luck i.e. the goodness of fit is bad as it doesn't fit the shape of the curve very well. Also tried another graphing program I have which has many other functions log fit, exponential fits etc all seem to fit very poorly. Also tried MS Excel linear fits etc. etc. No standard function seems to fit this data which is a synthetic hydrograph. If I get a good fitting function I can integrate the curve or route it through a reservoir using the solve function in Mathcad i.e. I would have to write a program using Eulers method etc which is prone to error. I seem to recall someone telling me that Mathematica had an advanced database of functions which it would try use one by one until it got the best match. Can genfit() do a similiar thing i.e. fins a function automatically? Forgive my ignorance is an interpolation the same as a continuous function in Mathcad i.e. can you do numerical integration on such a thing?
Mark