function v = npv(cf,r)
## Function v = npv(cf,r) returns the Net Present Value (npv) of the
## cash flow cf. The cash flow cf is received at the end of each
## period. The rate of return over the period is r. The parameter r
## is scalar. The cash flow cf is a (column) vector.
T = length(cf); # The number of periods.
pv = zeros(T,1); # Initialize present values (pv) at zero.
for t=1:T
pv(t) = cf(t) / (1+r)^t; # Set the pv's.
endfor
v = sum(pv); # npv is the sum of pv's.
endfunction