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[0] == 1, U12[0] == 0, U21[0] == 0, U22[0] == 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