bvls, a FORTRAN77 code which solves a least squares problem with bounds on the variables, by Charles Lawson and Richard Hanson.
Given an M by N matrix, A, and an M-vector, B, BVLS computes an N-vector X that solves the least-squares problem:
A * X = B
subject to BND(1,J) <= X(J) <= BND(2,J) for 1 <= J <= N.
The program allows the user to bound some or all of the variables. The user is also free to constrain some variables with only a one-sided bounded. The values BND(1,J) = -huge(ONE) and BND(2,J) = huge(ONE) are suggested choices to designate that there is no constraint in that direction. The parameter ONE is 1.0 in the working precision.
This algorithm is a generalization of the routine NNLS, which solves the least-squares problem:
A * X = B
subject to 0 <= X(J) for all J.
The subroutine NNLS appeared in 'Solving Least Squares Problems' by Lawson and Hanson, Prentice-Hall, 1974. Work on BVLS was started by Charles Lawson and Richard Hanson at Jet Propulsion Laboratory, 1973 June 12. Many modifications were subsequently made.
The original source code is available through NETLIB at
https://www.netlib.org/lawson-hanson/index.html.
bvls is available in a FORTRAN77 version and a FORTRAN90 version.
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Original Fortran77 version by Charles Lawson, Richard Hanson.