       Re: PDE & Complex solving problem

• To: mathgroup at smc.vnet.net
• Subject: [mg36491] Re: PDE & Complex solving problem
• From: Tom Burton <tburton at brahea.com>
• Date: Mon, 9 Sep 2002 00:29:30 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```On 9/8/02 12:22 AM, in article aleu3o\$557\$1 at smc.vnet.net, "Shz Shz Oon"
<OONSSHZ at hitachi.com.my> wrote:

> 1.) How to find the General Solution for below's partial differential
> equation?
> (y + u) du/dx + y (du/dy) = x - y
> ** I use "d" to represent the partial differential symbol.
> Can it be solved by function NDSolve in mathematica 4.1? How?

It's been a while, but I suspect that the presence of the nonlinear
convective term u du/dx alone makes a general solution unlikely. It's easy
to get a numerical solution for a particular set of boundary conditions, but
you are not guaranteed a solution. For instance, the following choice of a
and b are skirting failure, as the diagnostic contour plot shows.

Tom Burton

Needs["Graphics`Colors`"]

\!\(\(soln =
With[{a = \(-1\), b = 1.27, e = 0.001},
solutions =
NDSolve[{\((y + u[x, y])\)\ \[PartialD]\_x u[x, y] +
y\ \[PartialD]\_y u[x, y] == x - y, u[x, b] == 0,
u[a, y] == 0},
u, {x, a, 10}, {y, b, 10}]; \[IndentingNewLine]Plot3D[
Evaluate[u[x, y] /. \[InvisibleSpace]First[solutions]], {x, a,
10}, {y, b, 10},
PlotPoints \[Rule] 50]; \[IndentingNewLine]ContourPlot[
Evaluate[y + u[x, y] /. \[InvisibleSpace]First[solutions]], {x, a,
10}, {y, b, 10}, PlotPoints \[Rule] 50,
ColorFunction \[Rule] \((If[#1 > e, Green,
Red] &)\)]\[IndentingNewLine]];\)\)

```

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