Re: List manipulation?

*To*: mathgroup at smc.vnet.net*Subject*: [mg128319] Re: List manipulation?*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Sat, 6 Oct 2012 01:52:52 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net

On 10/5/12 at 2:48 AM, =?ISO-8859-1?Q?Andreas_Talmon_l=27Arm=E9e?= at smc.vnet.net wrote: >I got a problem with List manipulation. I have the following list >item: >a = -Subscript[50, 5] >and I would like to change the value of 50 to 360-50 and also change >the sign to +. First I tried to change the sign and then the value >and I got an outcome I didn't understand. Doing the other way round >I get the outcome I expected. Does anybody know what the difference >is? >Here is the Example file: http://dl.dropbox.com/u/4920002/Example.nb >a = -Subscript[50, 5] >a[[2, 1]] = 360 - a[[2, 1]] >a[[1]] = -1*a[[1]] >a >b = -Subscript[50, 5] >b[[1]] = -1*b[[1]] >b[[1]] = 360 - b[[1]] >b Compare a[[2, 1]] = 360 - a[[2, 1]] to b[[1]] = 360 - b[[1]] Do you not see you are setting a different part of the expression to 360-50? Also, your step to change the sign is needlessly complex. That is doing a = -a is sufficient as demonstrated by: In[4]:= b = -Subscript[50, 5]; a = -Subscript[50, 5]; b = -b; a[[1]] = -1*a[[1]]; {a, a == b} Out[8]= {Subscript[50, 5], True}