Re: Problem defining assumptions on a set of variables

*To*: mathgroup at smc.vnet.net*Subject*: [mg58073] Re: Problem defining assumptions on a set of variables*From*: dh <dh at metrohm.ch>*Date*: Fri, 17 Jun 2005 05:20:36 -0400 (EDT)*References*: <d8riof$ihp$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi Erik, see below, Daniel Koffijberg, H. wrote: > Hi all, > > I have encountered two problems using Mathematica v5.0 with parameters > for which no value is defined but for which some assumptions are defined. > I do not understand why each of the following statements return -1. > > Assuming[q\[Element]Reals&&q>0&&q<1, If[q > 3, 1, 0, -1]] > Refine[If[q > 3, 1, 0, -1],q\[Element]Reals&&q>0&&q<1] Assuming has no effect on "If[..]" only on functions like: Simplify,.. see manual. Therefore, "If" does his job without knowning about the assumptions, decides that q is not defined and returns -1. > > I would expect to get 0 as return value. What am I missing here ? > In addition I would like to define a fairly large matrix (e.g. 100x100) > in which each entry consists of a variable of unknown value. Something like: > [ p11 p12 p13, p14, ... , p1100 ] > [ p21 p22 p23, p24, ... , p2100 ] > ... > [ p1001 p1002 p1003, p1004, ... , p100100 ] Array is made for this job. E.g. Array[p,{100,100}] You assigne a value to an element by e.g.: p[3,4]=5 > > with pij the variable on row i column j. Any ideas on how to define such > a matrix without defining any values for the pij but with the added assumption > that 0 <= pij <= 1 for all the pij's ? > I want to use this matrix for computations in which I will provide values > for some of the variables and not provide values for the remaining variables > so that the result is expressed in terms of the undefined variables. However > the sets of defined / undefined variables will not be fixed so I'm looking for > a flexible solution. > > Any help will be greatly appreciated. > Erik Koffijberg. >