Subject: implicit diff & subst problems... /just to you.
From: dlakelan
Date: Thu, 06 Oct 2011 10:00:32 -0700
On 10/06/2011 09:02 AM, Evan Cooch wrote:
> Now, an earlier answer gave me a clue as to how to accomplish this in
> Maxima -- it looks (to me) like when I execute the following
>
>
> --> mat:matrix([0,s_a*m_2,s_a*m_3],[s_o,0,0],[0,s_a,0]);
> --> cp:charpoly(mat,lambda);
> --> depends(lambda,s_a);
> --> deriv:diff(cp,s_a);
> --> sol:solve(deriv,'diff(lambda,s_a));
>
>
> then what Maxima returns for sol is a vector, or some similar construct,
> where there is importance to the the LHS and RHS (which appear to be
> separately addressable), and that to use subst, you need to tell it to
> look/focus on the RHS, and ignore the LHS, where the LHS indicates that
> it is a derivative, which is true, but irrelevant to the purpose of
> numerically evaluating the function.
Maxima is giving you an equation (actually a list of equations, in case
there might be more than one solution), every equation has a left and a
right hand side. In this case, the left hand side tells you what was
solved for, and the right hand side tells you the solution. If you
substitute into the equation you will be substituting into both sides.
That is why you must take the right hand side before using subst to
evaluate.