Add notes to *GELST about how only exact rank-deficiency is checked

Author: GYT

SRC/cgelst.f

@@ -38,7 +38,16 @@
 *> CGELST solves overdetermined or underdetermined real linear systems
 *> involving an M-by-N matrix A, or its conjugate-transpose, using a QR
 *> or LQ factorization of A with compact WY representation of Q.
-*> It is assumed that A has full rank.
+*>
+*> It is assumed that A has full rank, and only a rudimentary protection
+*> against rank-deficient matrices is provided. This subroutine only detects
+*> exact rank-deficiency, where a diagonal element of the triangular factor
+*> of A is exactly zero.
+*>
+*> It is conceivable for one (or more) of the diagonal elements of the triangular
+*> factor of A to be subnormally tiny numbers without this subroutine signalling
+*> an error. The solutions computed for such almost-rank-deficient matrices may
+*> be less accurate due to a loss of numerical precision.
 *>
 *> The following options are provided:
 *>
@@ -163,7 +172,7 @@
 *>          = 0:  successful exit
 *>          < 0:  if INFO = -i, the i-th argument had an illegal value
 *>          > 0:  if INFO =  i, the i-th diagonal element of the
-*>                triangular factor of A is zero, so that A does not have
+*>                triangular factor of A is exactly zero, so that A does not have
 *>                full rank; the least squares solution could not be
 *>                computed.
 *> \endverbatim

SRC/dgelst.f

@@ -38,7 +38,16 @@
 *> DGELST solves overdetermined or underdetermined real linear systems
 *> involving an M-by-N matrix A, or its transpose, using a QR or LQ
 *> factorization of A with compact WY representation of Q.
-*> It is assumed that A has full rank.
+*>
+*> It is assumed that A has full rank, and only a rudimentary protection
+*> against rank-deficient matrices is provided. This subroutine only detects
+*> exact rank-deficiency, where a diagonal element of the triangular factor
+*> of A is exactly zero.
+*>
+*> It is conceivable for one (or more) of the diagonal elements of the triangular
+*> factor of A to be subnormally tiny numbers without this subroutine signalling
+*> an error. The solutions computed for such almost-rank-deficient matrices may
+*> be less accurate due to a loss of numerical precision.
 *>
 *> The following options are provided:
 *>
@@ -163,7 +172,7 @@
 *>          = 0:  successful exit
 *>          < 0:  if INFO = -i, the i-th argument had an illegal value
 *>          > 0:  if INFO =  i, the i-th diagonal element of the
-*>                triangular factor of A is zero, so that A does not have
+*>                triangular factor of A is exactly zero, so that A does not have
 *>                full rank; the least squares solution could not be
 *>                computed.
 *> \endverbatim

SRC/sgelst.f

@@ -38,7 +38,16 @@
 *> SGELST solves overdetermined or underdetermined real linear systems
 *> involving an M-by-N matrix A, or its transpose, using a QR or LQ
 *> factorization of A with compact WY representation of Q.
-*> It is assumed that A has full rank.
+*>
+*> It is assumed that A has full rank, and only a rudimentary protection
+*> against rank-deficient matrices is provided. This subroutine only detects
+*> exact rank-deficiency, where a diagonal element of the triangular factor
+*> of A is exactly zero.
+*>
+*> It is conceivable for one (or more) of the diagonal elements of the triangular
+*> factor of A to be subnormally tiny numbers without this subroutine signalling
+*> an error. The solutions computed for such almost-rank-deficient matrices may
+*> be less accurate due to a loss of numerical precision.
 *>
 *> The following options are provided:
 *>
@@ -163,7 +172,7 @@
 *>          = 0:  successful exit
 *>          < 0:  if INFO = -i, the i-th argument had an illegal value
 *>          > 0:  if INFO =  i, the i-th diagonal element of the
-*>                triangular factor of A is zero, so that A does not have
+*>                triangular factor of A is exactly zero, so that A does not have
 *>                full rank; the least squares solution could not be
 *>                computed.
 *> \endverbatim

SRC/zgelst.f

@@ -38,7 +38,16 @@
 *> ZGELST solves overdetermined or underdetermined real linear systems
 *> involving an M-by-N matrix A, or its conjugate-transpose, using a QR
 *> or LQ factorization of A with compact WY representation of Q.
-*> It is assumed that A has full rank.
+*>
+*> It is assumed that A has full rank, and only a rudimentary protection
+*> against rank-deficient matrices is provided. This subroutine only detects
+*> exact rank-deficiency, where a diagonal element of the triangular factor
+*> of A is exactly zero.
+*>
+*> It is conceivable for one (or more) of the diagonal elements of the triangular
+*> factor of A to be subnormally tiny numbers without this subroutine signalling
+*> an error. The solutions computed for such almost-rank-deficient matrices may
+*> be less accurate due to a loss of numerical precision.
 *>
 *> The following options are provided:
 *>
@@ -163,7 +172,7 @@
 *>          = 0:  successful exit
 *>          < 0:  if INFO = -i, the i-th argument had an illegal value
 *>          > 0:  if INFO =  i, the i-th diagonal element of the
-*>                triangular factor of A is zero, so that A does not have
+*>                triangular factor of A is exactly zero, so that A does not have
 *>                full rank; the least squares solution could not be
 *>                computed.
 *> \endverbatim