Re: NSolve Question
- To: mathgroup at smc.vnet.net
- Subject: [mg130864] Re: NSolve Question
- From: daniel.lichtblau0 at gmail.com
- Date: Wed, 22 May 2013 02:18:30 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- Delivered-to: l-mathgroup@wolfram.com
- Delivered-to: mathgroup-outx@smc.vnet.net
- Delivered-to: mathgroup-newsendx@smc.vnet.net
- References: <knerlt$3g$1@smc.vnet.net>
On Monday, May 20, 2013 11:03:09 PM UTC-5, Hagwood, Charles R wrote: > I have a known function f[x,y] and I want to solve the differential > > equation (1) for v[t], using NSolve > > partial [f(v[t],v'[t])/partial x +(d/dt)[partial f(v[t],v'[t])/partial y=0 (1) > > where v'[t] = derivative of v[t] with respect to t. > > I did a test to set up (1). I let > > f[x_,y_]:=x^2+y^3 > > v[t]:=Sin[t] > > g1[x_,y_]:=partial f(x,y)/partial x > > g2[x_,y_]:=partial f(x,y)/partial y > > g3[t_]:=g1[v[t],v'[t]]+D[g2[v[t],v'[t]],t] > > and asked Mathematica to evaluate > > g3[t] > > but, Mathematica gives an error. Thanks for the help > > Charles Hard to know exactly what you did because there is some traditional form, I guess, in what you show. My guess is the issue is in the definition of v[t_], wherein the pattern underbar was omitted. That would mess up the definition in a way that would make g3[t] give a bad result. Here is code that seems to work. f[x_,y_] := x^2+y^3 v[t_] := Sin[t] g1[x_,y_] := D[f[x,y],x] g2[x_,y_] := D[f[x,y],y] g3[t_] := g1[v[t],v'[t]]+D[g2[v[t],v'[t]],t] Then g3[t] gives Out[18]= 2 Sin[t] - 6 Cos[t] Sin[t] Daniel Lichtblau Wolfram Research