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