       Re: ntdvmm error

• To: mathgroup at smc.vnet.net
• Subject: [mg95513] Re: ntdvmm error
• From: dh <dh at metrohm.com>
• Date: Tue, 20 Jan 2009 05:49:08 -0500 (EST)
• References: <gkpps1\$doi\$1@smc.vnet.net>

```
Hi,

the problem comes from fpend[A_, B_] and fpendw[A_, B_]. E.g. look at:

fpend[0.001,0.1]. The equation to solve reads:

{-0.00001`+(w')[x]+(vz'')[x]==0,

-2 w[x]-(-6+w[x] (3+2 w[x]+2 w[x]^2))/(2 (10+2

w[x]^2+w[x]^4))-(vz')[x]==0,vz==0,(vz')==0.001`,w[0.5`]==0.1`}

note that we can easily solve the second eq. for (vz')[x]. If we

differentiate the resulting expression we get vz'', what allowes us to

eliminiate vz and get an equation for w:

{-0.00001+3 (w')[x]+((-6+w[x] (3+2 w[x]+2 w[x]^2)) (4 w[x] (w')[x]+4

w[x]^3 (w')[x]))/(2 (10+2 w[x]^2+w[x]^4)^2)-((3+2 w[x]+2 w[x]^2)

(w')[x]+w[x] (2 (w')[x]+4 w[x] (w')[x]))/(2 (10+2

w[x]^2+w[x]^4))==0,w[0.5]==0.1}

NDSolve will solve this easily.

Knowing w we can  solve the equation for vz.

Hope this helps, Daniel

SK wrote:

> Hi

>

> Im trying to solve two coupled nonlinear differential equations using

> the shooting method (see variables A and B). The file is can be

>

> http://web.mit.edu/~shahriar/Public/submission.nb

>

> When I run it I keep getting the error

> NDSolve::ntdvmm: Cannot solve to find an explicit formula for the

> derivatives.  NDSolve will try solving the system using a mass matrix

> method. >>

>

> and then Mathematica hangs and doesnt do anything.

> If I change Hz->0 for T, Mathematica solves it properly but it doesnt

> seem to like it when Hz is nonzero.

>

> Any help on getting past this error will be greatly appreciated

> Thanks

> S

>

```

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