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jf
03/31/12 5:55pm

Note the "many" in the reference page for NDSolve, under More Information:
"NDSolve can solve many differential-algebraic equations, in which some of the eqns are purely algebraic, or some of the variables are implicitly algebraic."

The equation starting with Sqrt[z[t]] is algebraic. The warning message says the method NDSolve uses for differential-algebraic equations handles real values only.

The equation starting with Sqrt[z[t]] is also wrong at t=0, since you get 0 == 339.583 I.

Can you re-arrange the equations to have just differential equations? For example, Solve the algebraic equation for Z[t], take the derivative, and include that as a third differential equation in the system.

references:
http://reference.wolfram.com/mathematica/tutorial/NumericalSolutionOfDifferentialEquations.html
http://reference.wolfram.com/mathematica/tutorial/NDSolveIDAMethod.html

For backing up a calculation that is going the wrong way (like taking T[t] negative) see:
http://www.wolfram.com/technology/guide/EventDetectionEventLocalization/



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Subject (listing for 'differential equations with conditions')
Author Date Posted
differential equations with conditions morrissey22 03/30/12 09:45am
Re: differential equations with conditions jf 03/31/12 5:55pm
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