Re: Reduce::inex problem
- To: mathgroup at smc.vnet.net
- Subject: [mg114361] Re: Reduce::inex problem
- From: Eduardo Cavazos <wayo.cavazos at gmail.com>
- Date: Thu, 2 Dec 2010 05:39:01 -0500 (EST)
On Wed, 2010-12-01 at 08:47 +0100, Andrzej Kozlowski wrote:
> Clearly Reduce does not like subscripts.
> {Vb == (4*Pi*rb^3)/3, Va == (4*Pi*ra^3)/3,
> V == Vb - Va, \[Rho] == m/V};
>
> % /. {rb -> 5.75, ra -> 5.7, \[Rho] -> 8.92};
>
> Reduce[%]
>
> Vb == 796.3282878380627 && Va == 775.7346243950061 &&
> V == 20.593663443056585 && m == 8.92*V
Ah yes... I've seen this before. Thanks for reminding me. :-)
Using subscripts can seemingly trip up Reduce sometimes. In this case,
the problem comes from mixing subscripted and non-subscripted V.
Here's a version with the subscripts which works; I just changed the 'V'
to an 'A':
{
Subscript[V, b] == 4/3*Pi*Subscript[r, b]^3,
Subscript[V, a] == 4/3*Pi*Subscript[r, a]^3,
A == Subscript[V, b] - Subscript[V, a],
\[Rho] == m/A
};
% /. {Subscript[r, b] -> 5.75,
Subscript[r, a] -> 5.70, \[Rho] -> 8.92};
Reduce[%, {m, A}]
And here's another where I changed 'V' to Subscript[V,total]. I.e. all
the instances of 'V' have subscripts:
{
Subscript[V, b] == 4/3*Pi*Subscript[r, b]^3,
Subscript[V, a] == 4/3*Pi*Subscript[r, a]^3,
Subscript[V, total] == Subscript[V, b] - Subscript[V, a],
\[Rho] == m/Subscript[V, total]
};
% /. {Subscript[r, b] -> 5.75,
Subscript[r, a] -> 5.70, \[Rho] -> 8.92};
Reduce[%, {m, Subscript[V, total]}]
Thanks again Andrzej.
Ed