Re: 2 quick questions

*To*: mathgroup at smc.vnet.net*Subject*: [mg112028] Re: 2 quick questions*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Wed, 25 Aug 2010 06:05:06 -0400 (EDT)

On 8/24/10 at 6:14 AM, lrebanks at netvigator.com (Lea Rebanks) wrote: >I have 2 quick questions regarding the Solve[Function]. >Firstly I wish to use Solve[eqns, {A, B}] on a simple system of >equations with missing variables A & B. >However I wish to constrain the results from Solve ... >1# - For all values of A and B to be positive values. >And >2# - One of the variables, say B, to be a positive integer. >Please could someone show me the correct coding for these 2 >requirements with a simple working example in both cases. If I wanted to add constraints on variables in equations, I would probably use Reduce rather than Solve. That is something like Reduce[And@@Flatten[{eqns, A>0,B>0,Element[B, Integers]}],{A,B}] for example In[10]:= eqns = {x^2 - 1 == 0, 2*x*y^2 == 200}; In[11]:= Reduce[ And @@ Flatten[{eqns, x > 0, y > 0, Element[y, Integers]}], {x, y}] Out[11]= x == 1 && y == 10