I need some help interpreting the behavior of the ev command.
I enter the expression:
(%i1) x_sho : A*sin(w*t) + B*cos(w*t)$
and then I want to setup equations for A and B in terms of x_sho(t=0) and vx_sho(t=0), where vx_sho = diff(x_sho,t).
A straightforward application of ev leads immediately to one of the two equations I want:
(%i2) IC1 : ev(x_sho,t=0) = x0;
(%o2) A=x0
however, my next attempt fails
(%i3) IC2 : ev(diff(x_sho,t),t=0);
diff: second argument must be a variable; found 0
-- an error. To debug this try debugmode(true);
I tried ev( ev(diff(x_sho,t),diff) , t=0 ), which also fails. A trivial workaround is available by defining an intermediate expression vx_sho = diff(x,t) and then using ev(vx_sho,t=0) so this isn't a serious problem however it is annoying and the process looks so much cleaner if I don't have to define vx.
Thanks,
Conrad