It is noteworthy that the segment of code that @ivanpribec made the topic of this thread occurs in Minpack-1. In one refactored version of Minpack-1, lines 793-803, we still see vestiges of this one-trip-do legacy, as well as the non-standard and unnecessary intrinsic DFLOAT, and see the intrinsic SUM rendered unavailable:
sum = zero
nm1 = n - 1
if (nm1 >= 2) then
do j = 2, nm1
sum = sum + dfloat(j)*x(j)
end do
end if
do i = 1, m
Fvec(i) = dfloat(i - 1)*sum - one
end do
Fvec(m) = -one
A manual refactoring into modern Fortran could have produced the more readable version:
sumj = sum([(j*x(j),j=2, n-1)])
fvec = [-1.0, ((i-1)*sumj - 1.0, i = 2, m-1), -1.0]
Note that this version rhymes better with the mathematical description from a journal article :
