Re: help on calculating sum of combinations

[Etienne Grossmann]

  Hello,

here is a very quick untested solution

function a = foo3 (A)
         A = A(:)';
         N = columns (A)
         B = zeros (N,2^N);   # Matrix of binary selection
         for i = 1:N
               B(i,:) = kron (kron (ones (1,2^(N-i)),[1 0]), ones (1,2^(i-1)));
         end
         B
         b = sum (B)

         C = (A'*ones(1,2^N)) .* B;  # Compute products
         C(find (C==0)) = 1;
         c = prod (C)

         a = zeros (1,N);            # Sum products
         for i = 1:2^N-1, a(b(i)) += c(i); end
end

         
  hth

  Etienne

On Wed, Oct 08, 2003 at 08:05:18AM +0530, sanjiv kapur wrote:
# hello
# i am a newbie for using octave (on rh9.0) ,though used a little matlab 
# before.may i request help in solving the problem as under,in case a 
# function has been developed by somebody.
# from a matrix or an array,i want to calculate the sum of various 
# combinations, i.e
# if A=[2, 3, 4,5]
# how do i get
#       a1=2+3+4+5
#       a2=2*3+2*4+2*5
#       a3=2*3*4+2*3*5+2*4*5+3*4*5
#       a4=2*3*4*5
# please guide me.
# thanks and regards
# sanjiv
# 
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-- 
Etienne Grossmann ------ http://www.isr.ist.utl.pt/~etienne



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