%%  illustrates vector/matrix operations
   
   b = [ 1 ; 2]
   
   C = [3 1; 1 3]
   
   b' * C * b
   
   % C being PSD means that all products like above are non-negative
   
   
   %% time trials
   
   b = normrnd(0,1,500,1);
   
    tic
   
   % for reps = 1:1000,
    total = 0; 
     for i = 1:length(b),     
       total = total + b(i);
     end 
   %end  
   toc
   
   %% now vectorized form
   
   
   one = ones(1,length(b));
   tic 
     sumb = one*b;
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   tic 
     sumb = sum(b);
   toc