Re: FindRoot and replacement rule
- To: mathgroup at smc.vnet.net
- Subject: [mg123929] Re: FindRoot and replacement rule
- From: Szabolcs Horvát <szhorvat at gmail.com>
- Date: Fri, 30 Dec 2011 07:09:49 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <jdh68h$kjj$1@smc.vnet.net>
On 2011.12.29. 8:52, SamTakoy wrote:
> Hi,
>
> Just wondering why FindRoot and other solvers return substitution
> rules rather than simply a list of solutions. What's the advantage?
>
If you have more than one variable, Mathematica needs a way to tell you
which value belongs to which variable.
Consider the following from the docs:
sol = Solve[a x + y == 7 && b x - y == 1, {x, y}]
If it simply returned {{8/(a + b), -((a - 7 b)/(a + b))}}, (using the
order of variables instead of explicit names), this would be a lot more
work to substitute back to the original equation.
With the current method equation /. sol[[1]] will substitute back the
first solution easily.
--
Szabolcs Horvát
Matheamtica QA site proposal: http://area51.stackexchange.com/proposals/37304