Linear Solution Question

[DrakeGis]

Hi,
  I'm solving a Linear ODE System, let say

  dU/dt = A * u(t)


and I have all the data in order to make it analytically,so in order to
know the solution at time t=1, I type...

t = 1;
A = [-1, 1;0,-2];
init = [0.5 ; sqrt(3)/2];
[S, D]=eig(A);
S*expm(D*t)*inv(S)*init

ans =

  0.38533
  0.11720

But If I want to "simulate" the system, I must calculate the solution at
each time... so for tiem t=1, I do

A*init

ans =

   0.36603
  -1.73205

Quite Diferent !!! Do you know what's wrong here ??

Thanks in Advance

  D.



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