RE: Newbie question about column sums of arrays

*To*: mathgroup at smc.vnet.net*Subject*: [mg68551] RE: [mg68508] Newbie question about column sums of arrays*From*: "Erickson Paul-CPTP18" <Paul.Erickson at Motorola.com>*Date*: Wed, 9 Aug 2006 04:20:17 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Seems a lot easier with the list of lists form of a matrix. Note, table and array use a somewhat different form of indexing. In[26]:= aa1 = Table[ x, {4},{4}] /. x:> (-1)^Random[Integer] Out[26]= {{-1,1,1,1},{-1,1,1,-1},{-1,1,-1,1},{1,1,1,-1}} In[27]:= Total[ aa1 ] Out[27]= {-2,4,2,0} In[28]:= %[[3]] Out[28]= 2 -----Original Message----- From: George W. Gilchrist [mailto:gwgilc at wm.edu] To: mathgroup at smc.vnet.net Subject: [mg68551] [mg68508] Newbie question about column sums of arrays I have spent several hours trying to find an answer to what must be an incredibly simple problem: how to sum the columns of an array containing a random mix of +1 and -1s. For example: In[7]:= AA1=Array[x, {4,4}]/. x:> (-1)^Random[Integer] Out[7]= \!\(\*FormBox[ RowBox[{"(", "\[NoBreak]", GridBox[{ {\(1[1, 1]\), \(1[1, 2]\), \(\((\(-1\))\)[1, 3]\), \(1[1, 4] \)}, {\(1[2, 1]\), \(1[2, 2]\), \(\((\(-1\))\)[ 2, 3]\), \(\((\(-1\))\)[2, 4]\)}, {\(1[3, 1]\), \(\((\(-1\))\)[3, 2]\), \(1[3, 3]\), \(1[3, 4] \)}, {\(\((\(-1\))\)[4, 1]\), \(1[4, 2]\), \(1[4, 3]\), \(\((\(-1\))\)[4, 4]\)} }, RowSpacings->1, ColumnSpacings->1, ColumnAlignments->{Left}], "\[NoBreak]", ")"}], TraditionalForm]\) In[8]:= Total[AA1] Out[8]= {(-1)[4,1]+1[1,1]+1[2,1]+1[3,1], (-1)[3,2]+1[1,2]+1[2,2]+1[4,2], (-1)[1,3]+(-1)[2,3]+1[3,3]+1[4,3], (-1)[2,4]+(-1)[4,4]+1[1,4]+1[3,4]} So, Total[] seems to do the right thing, but I cannot get the actual sums as real numbers, only this rather verbose representation. I have searched the manuals for just about everything I can think of with no luck. So, thanks for any help you can give me. Cheers, George .................................................................. George W. Gilchrist Email #1: gwgilc at wm.edu Department of Biology, Box 8795 Email #2: kitesci at cox.net College of William & Mary Phone: (757) 221-7751 Williamsburg, VA 23187-8795 Fax: (757) 221-6483 http://gwgilc.people.wm.edu/