probably I should not have written my question as a comment here
http://www.mapleprimes.com/forum/how-to-evaluate-faster, si I now put it as a new topic. Thanks for your time and help.

The problem is to evaluate as effectively as possible an n-fold sum of N additions, e.g., for n=3

FF := proc (N) options operator, arrow; evalhf(add(add(add((1/2*1/3*1/4)*(1/2)^j*(3/4)^g*(2/3)^i/(.4*i+.4+.1*j+.1+.3*g+.3), i = 0 .. N), j = 0 .. N), g = 0 .. N)) end proc

In one of the good books on Maple, an advice was to use external text editor of your choice if yoru code is likely to be more than 10 lines. I know there are WinEdt for laTex, RWinEdt , TinnR or Emacs for R, but what  is best for Maple? What will highlight Maple syntacis, commands, etc? What's available and what's good?  Thanks.

In menu Options/Interface I chose to open worksheets as a new tab. That's convenient. However, I cannot figure out how to make Maple 11 start up with the same set of tabs/worksheets automatically loaded when I turn on my PC to use Maple next time. Thanks.

 

What would be an effective way to code a sequence of numbers Y(t):=Poisson random variable with mean X(t) and X(t):=M+phi*X(t-1)+alpha*(Y(t-1)-X(t-1)) for 0<alpha<phi<1, M>0? Thanks.

I need to evaluate expression

sum((sum((sum((1-p)^i/(a[1]*i+a[1]+a[2]*j+a[2]+a[3]*k+a[3]), i = 0 .. infinity))*(1-p)^j, j = 0 .. infinity))*(1-p)^k, k = 0 .. infinity).

A straightforward evalf(subs(a[1] = .4, a[2] = .1, a[3] = .5, p = 1/3, %)) is too too slow. Are there any faster solutions? Thanks in advance.