Applying function only if the output is positive

*To*: mathgroup at smc.vnet.net*Subject*: [mg116290] Applying function only if the output is positive*From*: ma07llg2 <lou2k4 at msn.com>*Date*: Thu, 10 Feb 2011 05:20:49 -0500 (EST)

Hi, I am trying to find a way which will only apply my function if the output is positive, this is what i have but when the numbers become negative i need them to not be included anymore. update1[x_List] := x + j.n[x] + Table[RandomReal[{-.5, .5}], {k, 1, Length[x]}] w1[k_] := NestList[update1, gg, k] w1[2] {{0.261588, 0.512798, 0.709287, 0.914866, 0.779221, 0.00614278, 0.904256, 0.95166, 0.670016, 0.901556}, {0.427219, 0.656549, 0.825981, 1.38668, 0.667352, -0.0109928, 0.78814, 0.458776, 0.276835, 1.40125}, {-0.00600954, 0.831096, 1.58705, 2.69087, 1.12829, -0.0721115, 0.562469, 0.343643, 0.947323, 2.76569}} Is this possible? any help would be really appreciated! Thanks