Problems with a first order differential equation

*To*: mathgroup at smc.vnet.net*Subject*: [mg123282] Problems with a first order differential equation*From*: Pippo <dinodeblasio at yahoo.it>*Date*: Wed, 30 Nov 2011 03:21:00 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

Dear all, I have a list of values (2-dimensional). data={{xi,yi}...} And I finally am able to fit them as the example below: and find the parameters A and B ----------------------------------- Clear[y]; data = {{1, 0.033}, {2, 0.054}, {5, 0.088}}; With[{C = 1/9}, Column[{ model = DSolve[ {y'[t] == -A (y[t])^2 + B (C - y[t]), y[0] == 0}, y[t], t][[1]], param = FindFit[data, y[t] /. model, {A, B}, t], Plot[y[t] /. model /. param, {t, 0, Max[data[[All, 1]]]}, ImageSize -> 400, AxesLabel -> {"t", "y[t]"}, Epilog -> {Red, AbsolutePointSize[5], Point[data]}]}]] // Quiet --------------------------- Thanks to Bob Hanlon. However I would like to fit the same data by using different exponents of the term y[t])^2 which appear on the right hand side of the differential equation: for example I'd like to use: {y'[t] == -A (y[t])^3 + B (C - y[t]), y[0] == 0}, or {y'[t] == -A (y[t])^(2.5) + B (C - y[t]), y[0] == 0}, Is that anyway to fit a list of two-dimensional by using the models above? Thanks. Dino