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Re: ntdvmm error

  • To: mathgroup at
  • Subject: [mg95513] Re: ntdvmm error
  • From: dh <dh at>
  • Date: Tue, 20 Jan 2009 05:49:08 -0500 (EST)
  • References: <gkpps1$doi$>


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:


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


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 


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

> downloaded at




> 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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