Subject: Fw: Problem with subst() after diff() - FIXED
From: Lut Mentz
Date: Mon, 14 Mar 2011 02:08:40 -0000
I realized it is the 'diffs in the expression that cause the problem.
----- Original Message -----
From: "Lut Mentz" <lut.mentz at zen.co.uk>
To: <maxima at math.utexas.edu>
Sent: Monday, March 14, 2011 1:57 AM
Subject: Problem with subst() after diff()
> This little script
>
> assume(l>0);
> assume(t>0);
> Q:G*M*l*v*t/(2*(l^2+(v*t)^2)^(3/2));
> depends(v,t);
> D2Q:diff(Q,t,2);
> subst(0,t,D2Q);
>
> crashes on the last line ...
>
> ..
> ..
> (%i4) depends(v,t)
> (%o4) [v(t)]
> (%i5) D2Q:diff(Q,t,2)
> (%o5) [ snipped long expression]
> (%i6) subst(0,t,D2Q)
> Attempt to differentiate with respect to a number:
> 0
> -- an error. To debug this try debugmode(true);
>
> I'm baffled. I thought the differentiating was done. Any help appreciated.
>
> Lut Mentz