### Linear Least Squares (LLS) Problems

?gels uses QR or LQ factorization to solve an overdetermined or underdetermined linear system with a full rank matrix.
``` call sgels (trans, m, n, nrhs, a, lda, b, ldb, work, lwork, info) call dgels (trans, m, n, nrhs, a, lda, b, ldb, work, lwork, info) call cgels (trans, m, n, nrhs, a, lda, b, ldb, work, lwork, info) call zgels (trans, m, n, nrhs, a, lda, b, ldb, work, lwork, info) ```

?gelsy computes the minimum-norm solution to a linear least squares problem using a complete orthogonal factorization of A.
``` call sgelsy (m, n, nrhs, a, lda, b, ldb, jpvt, rcond, rank, work, lwork, info) call dgelsy (m, n, nrhs, a, lda, b, ldb, jpvt, rcond, rank, work, lwork, info) call cgelsy (m, n, nrhs, a, lda, b, ldb, jpvt, rcond, rank, work, lwork, rwork, info) call zgelsy (m, n, nrhs, a, lda, b, ldb, jpvt, rcond, rank, work, lwork, rwork, info) ```

?gelss computes the minimum-norm solution to a linear least squares problem using the singular value decomposition of A.
``` call sgelss (m, n, nrhs, a, lda, b, ldb, s, rcond, rank, work, lwork, info) call dgelss (m, n, nrhs, a, lda, b, ldb, s, rcond, rank, work, lwork, info) call cgelss (m, n, nrhs, a, lda, b, ldb, s, rcond, rank, work, lwork, rwork, info) call zgelss (m, n, nrhs, a, lda, b, ldb, s, rcond, rank, work, lwork, rwork, info) ```

?gelsd computes the minimum-norm solution to a linear least squares problem using the singular value decomposition of A and a divide and conquer method.
``` call sgelsd (m, n, nrhs, a, lda, b, ldb, s, rcond, rank, work, lwork, iwork, info) call dgelsd (m, n, nrhs, a, lda, b, ldb, s, rcond, rank, work, lwork, iwork, info) call cgelsd (m, n, nrhs, a, lda, b, ldb, s, rcond, rank, work, lwork, rwork, iwork, info) call zgelsd (m, n, nrhs, a, lda, b, ldb, s, rcond, rank, work, lwork, rwork, iwork, info) ```

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