Thank you for your reply. I tried your method, however, when the program goes to "u1 := int(int(convert(sin(omega*(ts+ys/ct))*Heaviside(t-ts-ys/ct), piecewise, t),
 ys = H-cl*ts .. ct*ts), ts = H/(cl+ct) .. (H+cl*tau[l])/(cl+ct));", it just kept evaluating without giving me any result. Is that because I am using a different version of maple? I am using Maple 12.

Here is my orignal file "test" and modified file "test.m". Really appreciate your help.

test.mw   test_m.mw