#
#       function [fp,pc,ac,np] = percent(f)
#
#  Compute percentages and cumulative percentages from a vector f.
#  We assume that f (usually the output of eig+sort) contains a
#  decreasing sequence of positive numbers and possibly one or more
#  zeros. Negative entries are discarded.
#
#  Input:
#     f (a row vector)
#
#  Output:
#
#     fp = the first part of f, containing only positive entries.
#     pc = row vector containing percentages (of each entry in
#          f with respect to the sum of all (positive) entries).
#     ac = row vector containing cumulative percentages
#     np = number of positive entries in f (equal to the length
#        of fp, pc and ac)
#
function [fp,pc,ac,np] = percent(f)
    eps1=1.e-9;
    [m,n]=size(f);
    ac=zeros(1,n);
    t=0;np=n;
    for ni=1:n
       if f(ni)>eps1
          t=t+f(ni);
          ac(ni)=t;
       else
          np=ni-1;
          break;
       endif
    endfor
    fp=f(1:np);
    pc=fp*100/t;
    ac=ac(1:np)*100/t;
    disp(["*** percent: Found " num2str(n-np) " nonpositive elements"]);
endfunction