The semantics of ev are strange and curious. Read the documentation for ev
if you want the full and ugly details. But I would recommend instead that
you avoid ev as much as possible, and use subst as appropriate.
-s
On Sat, Mar 30, 2013 at 2:04 PM, Thomas D. Dean <tomdean at speakeasy.org>wrote:
> kill(all);
> depends(u,t,v,u);
> eq1:v=F(u);
> eq2:u=G(t);
> soln:diff(eq1,t); /* need to assign soln before ev */
>
> ev(soln,diff(eq2,t),F(u)=v,G(**t)=u);
>
> ev(diff(eq1,t),diff(eq2,t),F(**u)=v,G(t)=u);
>
> Why the difference?
>
> My guess is that in the first instance, assignment to soln fully evaluates
> soln where in the 2nd instance something different happens.
>
> Tom Dean
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