Re: Re: More /.{I->-1} craziness

*To*: mathgroup at smc.vnet.net*Subject*: [mg106101] Re: [mg106036] Re: More /.{I->-1} craziness*From*: DrMajorBob <btreat1 at austin.rr.com>*Date*: Fri, 1 Jan 2010 05:36:56 -0500 (EST)*References*: <hhf5s3$h4o$1@smc.vnet.net> <200912310813.DAA24663@smc.vnet.net>*Reply-to*: drmajorbob at yahoo.com

Of those examples, the one I find most amazing is a .3.4/.3->c FullForm@% a 0.3.4 Times[a,Dot[0.3`,4]] The result is bizarre, and it can't be entered at the keyboard. Try entering 0.3.4 in an Input cell, and see what happens! Bobby On Thu, 31 Dec 2009 02:13:51 -0600, Richard Fateman <fateman at cs.berkeley.edu> wrote: > AES wrote: >> The more I play with these I->-I substitution rules, the more seemingly >> wildly inconsistent results emerge. For example: >> >> In[1]:= -I/.I->-I >> >> Out[1]= -I >> > ..snip.. >> > These examples you give are perfectly consistent with a certain world > view which is that I is not a symbol, but a functional form, > Complex[0,1], and -I is a different form, Complex[0,-1]. > > The fact that this is not what you expect as a mathematician is simply > your fault.:) > > You might find these examples. some old, some new, confusing as well. > (in Mathematica 6.0) > > Here are some puzzles for you. Guess what they return. (Answers below) > 3 /. 3->4 > 3 /.3->4 > 3 /0.3->4 (which helps explain previous line) > > 3 / . 3 ->4 > > 3 /. 3.0->4 > > 3/.3.0->4 > 3.0/. 3.0->4 > > a. 3/. a->b > a.3 /. a->b > > a .3 . 4 /. 3 -> c > a. 3 . 4 /. 3 -> c > > .......answers......... > > 3 /. 3->4 returns 4 > 3 /.3->4 returns 10.->4 > 3 /0.3->4 returns 10.->4 (which helps explain previous line) > > 3 / . 3 ->4 syntax error > > 3 /. 3.0->4 returns 3 > > 3/.3.0->4 returns 0.->4 > 3.0/. 3.0->4 returns 4 > > a. 3/. a->b returns b.3 > a.3 /. a->b returns 0.3*b > > a .3 . 4 /. 3 -> c returns a 0.3.4 > a. 3 . 4 /. 3 -> c returns a.c.4 > > > > > and yes, I know the explanation for all of these. > -- DrMajorBob at yahoo.com