Re: desperate, please help.

*To*: mathgroup at smc.vnet.net*Subject*: [mg27374] Re: desperate, please help.*From*: "Allan Hayes" <hay at haystack.demon.co.uk>*Date*: Thu, 22 Feb 2001 02:25:20 -0500 (EST)*References*: <97003k$tq@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

There are several syntax errors, but even when they have been corrected the equation is not solved. However, algebraic equations are simply dealt with rhs=-F/r[x]//. { T[x]->330+43.3*x,F->.9*163,C->9.3, k[x]->31.1Exp[7906*(T[x]-360)/(T[x]*360)], K[x]->3.03*Exp[-830.3*((T[x]-333)/(T[x]*333))], r[x]->-k[x]*C*(1-(1+1/K[x])*x) } 0.5072087957680738/ (E^((3953*(-30 + 43.3*x))/(180*(330 + 43.3*x)))* (1 - (1 + 0.33003300330033003* E^((2.493393393393393*(-3 + 43.3*x))/ (330 + 43.3*x)))*x)) With this the problem reduces to the following, which Mathematica quickly solves NDSolve[{v'[x] == rhs, v[0] == 0}, {v}, {x, 0, .7}]; Look at the plot. Plot[v[x] /. %, {x, 0, 0.7}] -- Allan --------------------- Allan Hayes Mathematica Training and Consulting Leicester UK www.haystack.demon.co.uk hay at haystack.demon.co.uk Voice: +44 (0)116 271 4198 Fax: +44 (0)870 164 0565 "Thjqase" <thjqase at aol.com> wrote in message news:97003k$tq at smc.vnet.net... > I need help numerically solving a differential equation coupled with several > algebraic equations. New to Mathematica. Here's code: > > NDSolve[{v'[x] == -F÷r, T[x] == 330 + 43.3*x, F = .9*163, C == 9.3, > k[x] == 31.1Exp(7906*(T - 360)/(T*360)) > , K[x] == 3.03*Exp(-830.3*((T - 333)/(T*333))), > r[x] == -k*C*(1 - (1 + 1/K)*x), > v[0] == 0}, {v} > , {x, 0, .7}] > > Error code is: > > NDSolve::"deql": "The first argument must have both an equation and an \ > initial condition." > > Any suggestions? What am I doing wrong? My head is sore from banging it against > the wall. > > TIA. >