Re: problem with append

*To*: mathgroup at smc.vnet.net*Subject*: [mg129540] Re: problem with append*From*: <bar at robox.ii.up.krakow.pl>*Date*: Mon, 21 Jan 2013 00:10:22 -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*References*: <kdg2kv$hf8$1@smc.vnet.net>

Paolo cachecho <paolocach at gmail.com> 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 > Try this: r = {}; For[a = 2, a < 6, a++, For[b = 2, b < 6, b++, AppendTo[rr, a^b]]] rr or Table[ Table[a^b, {b, 2, 5}], {a, 2, 5}] Table[a^b, {a, 2, 5}, {b, 2, 5}] but it is not the same, I'm not sure what You mean remember : Table is faster then For , AppendTo is extremally slow see http://blog.wolfram.com/2011/12/07/10-tips-for-writing-fast-mathematica-code/ Try examples: n = 200; rr = {}; Timing@For[a = 2, a < n, a++, For[b = 2, b < n, b++, AppendTo[rr, a + b]]] {18.4572, Null} and Timing[rr = Table[a + b, {a, 2, n - 1}, {b, 2, n - 1}];] {0.104007, Null} (I changed a^b -> a+b ) Olaf,