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.
>