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jf
02/27/12 8:12pm

NDSolve has to calculate y''[0] to get started. It delegates the job of separating out y'' to Solve.


In[1]:= Solve[ -y''[x]*x^2 - y'[x]*x + x^2*y[x]^3 + (-x^2 + 1)*y[x] == 0 , y''[x] ]




Out[1]= {{y''[x] ->

y[x] - x^2 y[x] + x^2 y[x]^3 - x y'[x]
-------------------------------------------}}
x^2

When NDSolve substitutes in x==0, it sees a division by zero.


The second message,
Infinity::indet: "Indeterminate expression 0. ComplexInfinity encountered."
means that the numerator was zero, too. NDSolve does not have a way of canceling zeros.

One workaround is to cheat and manually insert a value for y''[0]. Around x=0, the If gives a fixed value for y''. Once x has moved away from 0 by even a small amount, the regular equation takes over.

In[6]:= NDSolve[{ -y''[x]==
If[x==0.,0.1,(y[x]-x^2 y[x]+x^2 y[x]^3 - x y'[x])/x^2],
y[0]==0,y'[0]==1},y,{x,0,10}]

Out[6]= {{y->InterpolatingFunction[{{0.,10.}},<>]}}

In[7]:= Plot[ y[x]/. %,{x,0,10}]


The attached notebook has the code and plot.

Attachment: zerodiv27810.nb, URL: ,

Subject (listing for 'Non linear differential equation')
Author Date Posted
Non linear differential equation Lorentz 02/25/12 12:29pm
Re: Non linear differential equation Nasser M. Ab... 02/26/12 8:56pm
Re: Non linear differential equation jf 02/27/12 8:12pm
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