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NDSolve a system of differential equations with initial conditions?

POSTED BY: Jose Calderon
6 Replies
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Coding Geeks
Coding Geeks
Posted 3 years ago
POSTED BY: Coding Geeks

The code

ClearAll["Global`*"]
\[Nu] = 5*10^-5;
k = 2*\[Pi]*\[Nu];
sol = NDSolve[{\[Nu]*u''[y] + k*(y)^2*Abs[u'[y]]*u''[y] == 0, 
   u[0] == 0, u'[0.999553801] == 0}, u, {y, 0, 0.999553801}]

works fine for me. It gives the null function.
POSTED BY: Gianluca Gorni
POSTED BY: Neil Singer

Jose,

Gianluca is correct. Your initial conditions should look something like this:

sol = NDSolve[{x'''[t] == y'[t] x[t], 
   y''[t] == -(1/(x[t]^2 + y[t]^2)), x[0] == 1, x''[0] == 1, 
   x'[0] == 1, y'[0] == 0, y[0] == 0}, {x, y}, {t, 0, 100}]

Regards,

Neil
POSTED BY: Neil Singer

Thank you.. I made up the DE problem . I am looking to test how NDsolve does works. I have made another correction but still don't know why I am no getting anywhere.
POSTED BY: Jose Calderon

The condition x'''[0] == 0 is superfluous, because it is a consequence of the first equation and of y'[0] == 0. The condition y''[0] == 0 is not compatible with the second equation.
POSTED BY: Gianluca Gorni
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