Re: NDSolve and error

*To*: mathgroup at smc.vnet.net*Subject*: [mg92565] Re: NDSolve and error*From*: "M.G. Bartlett" <marshall.bartlett at gmail.com>*Date*: Mon, 6 Oct 2008 04:12:25 -0400 (EDT)*References*: <gc7fql$elo$1@smc.vnet.net>

On Oct 5, 12:16 am, doda... at poczta.fm wrote: > Hello! > Lately I wrote simple code in Mathematica > > sol[p_] := > NDSolve[{Sqrt[ > 1 + (y'[t])^2] == (x^(p - 1) + (y[x])^(p - 1)*y'[= x])/(x^p + > y[x]^p)^(1 - 1/p), y[1] == 6}, y, {x,= 1, 4}] > > but when I typed sol[2] the following kind of error was shown: > > NDSolve::"ndnum": "Encountered non-numerical value for a derivative at > \ > \!\(x\) == \!\(4.587812868332132`*^-296\)." > > May I know what I'm doing wrong? Or how can I improve that code to > work correctly? > Thank you in advance > John John, I think your error results from the fact that you have defined y as both a function of x and as a function of t (y[t] and y[x]). I am not certain if you meant for y to be a function of both (in which case you need to specify it as such (y[x,t]) throughout the equation (and specify which derivatives you are taking) or if the y[t] on the left side of your differential equation should be a y[x] (leaving you with a tractable ordinary differential equation). Hope that helps, Marshall