Re: problem with reduce

*To*: mathgroup at smc.vnet.net*Subject*: [mg100431] Re: problem with reduce*From*: dh <dh at metrohm.com>*Date*: Wed, 3 Jun 2009 05:28:15 -0400 (EDT)*References*: <h00d04$phb$1@smc.vnet.net>

Hi, consider the equation: jP == j - C[2]]. As j does not appear anywhere else j and jp are completely undetermined. Now consider: i == 1 + C[1] && N == 1 + C[1] + C[2]. As i and N do not appear anywhere else, these equation do not add any info. Finally: iP == 1 + C[1] + C[2] simply says that ip is an integer >=1. Therefore, the solution is: ip is an integer >=1 and jP an arbitrary number. Daniel olfa wrote: > Hi mathematica community, > I have to solve this example > In[88]:= Reduce[Exists[{C[1], C[2]}, > Element[{C[1], C[2]}, Integers] && C[1] >= 0 && C[2] >= 0 && > i == 1 + C[1] && N == 1 + C[1] + C[2] && iP == 1 + C[1] + C[2] && > jP == j - C[2]], {iP, jP}, Backsubstitution -> True] > > During evaluation of In[88]:= Reduce::nsmet: This system cannot be > solved with the methods available to \ > Reduce. >> > > I have observed that when I remove Element[{C[1], C[2]}, Integers] && C > [1] >= 0 && C[2] >= 0 like that: > In[89]:= Reduce[ > Exists[{C[1], C[2]}, > i == 1 + C[1] && N == 1 + C[1] + C[2] && iP == 1 + C[1] + C[2] && > jP == j - C[2]], {iP, jP}, Backsubstitution -> True] > > it gives me an output which is: > > Out[89]= iP == N && jP == i + j - N > > > I need to keep the information that Element[{C[1], C[2]}, Integers] && > C[1] >= 0 && C[2] >= 0 but reduce tells me that it cannot solve this > system. why and how to deal with this problem? > thank you. >