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Student Support Forum: 'NDSolve issue' topicStudent Support Forum > General > "NDSolve issue"

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Amanda
04/11/13 4:43pm

NDSolve[{j'[t] == -5 j[t] + 3 k[t] j[t], k'[t] == -3 k[t] + 2 j[t] k[t],
j[0] == 2, k[0] == 3}, {j[t], k[t]}, {t, 0, 10}]

I'm having a problem with the coding of NDSolve. When you put in certain initial values such as the one above, you get the warning "step size is effectively zero; singularity or stiff system suspected".

This has happened several times using different equations. But works with other equations. [Like the coding below.]
NDSolve[{x'[t] == 9 x[t] - 2 (x[t])^2 - 4 x[t] y[t],
y'[t] == 8 y[t] - 5 x[t] y[t] - 3 (y[t])^2, x[0] == 1,
y[0] == 1/2},
{x[t], y[t]}, {t, 0, 10}]

Why is this happening? Are there specific initial values that need to be used? Why do some work while others don't?


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Subject (listing for 'NDSolve issue')
Author Date Posted
NDSolve issue Amanda 04/11/13 4:43pm
Re: NDSolve issue jf 04/11/13 7:28pm
Re: Re: NDSolve issue Amanda 04/11/13 7:39pm
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