Re: differential equation solve

*To*: mathgroup at smc.vnet.net*Subject*: [mg68851] Re: differential equation solve*From*: Peter Pein <petsie at dordos.net>*Date*: Mon, 21 Aug 2006 03:28:02 -0400 (EDT)*References*: <ec97f9$4bn$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

elvis schrieb: > Here we often use mathematica to solve differential equations, when I > encouter a equation with several constrains I set them to those values. > But it cannot solve it and have the following warnings: > > DSolve::deqx: Supplied equations are not differential equations of > the given functions. > > Give a very simple differential equation here: > > DSolve[{y'[x] == r*y[x], y[0] == a}, y, x] > > another equation: > > \!\(DSolve[{\(x'\)[t] == r*x[t] \((1 - x[t]\/xm)\), x[0] == x0}, x, > t]\) > > this face anothe prolbem > > Can anyone help to "solve" this problem for me? > Thanks! > Do you use Mathematica 0.1 alpha? Even this one solves these equations: $Version "4.0 for Microsoft Windows (July 16, 1999)" DSolve[{Derivative[1][y][x] == r*y[x], y[0] == a}, y, x] {{y -> (a*E^(r*#1) & )}} DSolve[{Derivative[1][x][t] == r*x[t]*(1 - x[t]/xm), x[0] == x0}, x, t] {{x -> ((E^(r*#1)*x0*xm)/(-x0 + E^(r*#1)*x0 + xm) & )}} and so does 5.1 for Windows: {{y -> Function[{x}, a*E^(r*x)]}} {{x -> Function[{t}, (E^(r*t)*x0*xm)/ (-x0 + E^(r*t)*x0 + xm)]}} Peter