Problem with NDSolve

• To: mathgroup at smc.vnet.net
• Subject: [mg17233] Problem with NDSolve
• From: "Kevin J. McCann" <kevinmccann at Home.com>
• Date: Fri, 30 Apr 1999 02:34:31 -0400
• Organization: @Home Network
• Sender: owner-wri-mathgroup at wolfram.com

```I am trying to solve a set of coupled DE's with NDSolve.  I have been
getting an extremely frustrating
error message with the following:

rho= 10;
sol =
NDSolve[{I a1'[t] == v[[1,1]] a1[t],
mu x''[t] == 0.,
mu z''[t] == 0.,
z[0] == -zmax, z'[0] == v,
x[0] == rho, x'[0] == 0.,
a1[0] == 1.}, {x[t], z[t], a1[t]}, {t, 0., 1},
MaxSteps -> 20000, AccuracyGoal -> 5,
PrecisionGoal -> 5, MaxStepSize -> 10.];

NDSolve::"ndnum":
"The right-hand side of the differential equation does not evaluate to a
\
number at \!\(t\) == \!\(0.`\)."

v is actually a matrix that is part of the real problem I am trying to
solve, but v[[1,1]]  is a real-
valued Interpolating Function.  Now here is the truely strange part.  If I
remove the "I" in front of the a1'[t]
in the first DE, the thing runs!

Maybe I should just change the problem I am trying to solve?!

Any ideas?

Thanks,

Kevin

```

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