Re: problem with append

*To*: mathgroup at smc.vnet.net*Subject*: [mg129531] Re: problem with append*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Mon, 21 Jan 2013 00:07:22 -0500 (EST)*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 1/20/13 at 1:21 AM, paolocach at gmail.com (Paolo cachecho) wrote: >hello i am new to mathmatica.i have the following problem if anyone >could help. >For[a = 2, a < 6, a++, >For[b = 2, b < 6, b++, Appendto[rr = {}, a^b]]] >rr >but rr remains empty. how can i solve this thank you There are two issues with the code above. First you set rr to a null list for every value of a,b. Second, Appendto should be AppendTo. This will do what you want rr={}; For[a = 2, a < 6, a++, For[b = 2, b < 6, b++, AppendTo[rr, a^b]]] A faster more efficient way to get the same result would be rr = Flatten@Outer[#1^#2&, Range[2,5],Range[2,5]] or rr = Flatten@Table[a^b,{a,2,5},{b,2,5}] Using For generally results in slower running Mathematica code. AppendTo copies the entire array to add another element which will consume more memory and cpu resources.