Re: Re: What is happening here? (TagSet)
- To: mathgroup at smc.vnet.net
- Subject: [mg28140] Re: [mg28117] Re: What is happening here? (TagSet)
- From: BobHanlon at aol.com
- Date: Sun, 1 Apr 2001 00:08:03 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
I can only guess. While Im[x] = 0 is equivalent to Re[x] = x and Abs[x] = x and Arg[x] = 0 it is just as true that Re[x] = x or Abs[x] = x or Arg[x] = 0 is equivalent to Im[x] = 0. Consequently, trying to account for all the logical consequences of any of these statements would readily lead to an infinite loop unless numerous additional checks were built in to avoid such complications. It is undoubtedly much easier to let the user enter definitions with TagSet or use explicit assumptions (e.g., Element[x, Reals]) as required by the problem at hand. Bob Hanlon In a message dated 2001/3/31 3:50:11 AM, johntodd at fake.com writes: >To the quick of the matter: Mathematically speaking, if one states >that the imaginary part of a number is zero, then that only leaves the >real part, which could then be any real number. It seems redundant >that once one has defined the imaginary part of a number to be zero, >that one must further stipulate that the real part of the number is in >essence real (i.e. itself). What is the reason for Mathematica >insisting that the additional upvalues for x and y be defined in order >to get the mathematically consistent results one would expect? >