       Why doesn't DSolve solve this?

• To: mathgroup at smc.vnet.net
• Subject: [mg53064] Why doesn't DSolve solve this?
• From: mmandelberg at comcast.net
• Date: Wed, 22 Dec 2004 04:53:00 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```This is a relatively simple set of four first order coupled linear
differential equations:

DSolve[{I U11'[t] == U11[t] + t U21[t],
I U12'[t] == U12[t] + t U22[t],
I U21'[t] == t U11[t] + U21[t],
I U22'[t] == t U12[t] + U22[t],
U11 == 1, U12 == 0, U21 == 0, U22 == 1},
{U11[t], U12[t], U21[t], U22[t]}, t]

With solution:

U11[t] = U22[t] = Exp[-I t(2+t)/2](1+Exp[I t^2])/2
U21[t] = U12[t] = Exp[-I t(2+t)/2](1-Exp[I t^2])/2

But Mathematica just gives me my input right back. Am I doing something
wrong?

Thanks

Michael Mandelberg

```

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