solve_linear_system() now returns *reciprocal* condition number

git-svn-id: http://svn.einsteintoolkit.org/cactus/EinsteinAnalysis/AHFinderDirect/trunk@1083 f88db872-0e4f-0410-b76b-b9085cfa78c5

2 files changed, 10 insertions, 9 deletions

diff --git a/src/elliptic/dense_Jacobian.cc b/src/elliptic/dense_Jacobian.cc
index 4fd9e66..e5cec64 100644
--- a/src/elliptic/dense_Jacobian.cc
+++ b/src/elliptic/dense_Jacobian.cc
@@ -199,8 +199,9 @@ delete[] pivot_;
 //
 // This function solves the linear system J.x = rhs, with rhs and x
 // being nominal-grid gridfns, using LAPACK LU-decomposition routines.
-// It returns the estimated infinity-norm condition number of the linear
-// system, or 0.0 if the matrix is numerically singular
+//
+// It returns the (infinity-norm) estimated reciprocal condition number
+// of the linear system.
 //
 fp dense_Jacobian__LAPACK::solve_linear_system
 	(int rhs_gfn, int x_gfn,
@@ -272,9 +273,7 @@ fp rcond;
 #else
   #error "don't know fp datatype!"
 #endif
-if (rcond == 0.0)
-   then return 0.0;					// *** ERROR RETURN ***
-							// *** (singular matrix)
-return 1.0/rcond;
+
+return rcond;
 }
 #endif	// HAVE_DENSE_JACOBIAN__LAPACK
diff --git a/src/elliptic/dense_Jacobian.hh b/src/elliptic/dense_Jacobian.hh
index 6946993..cf0b8ba 100644
--- a/src/elliptic/dense_Jacobian.hh
+++ b/src/elliptic/dense_Jacobian.hh
@@ -87,9 +87,11 @@ public:
 	// solve linear system J.x = rhs via LAPACK
 	// ... rhs and x are nominal-grid gridfns
 	// ... overwrites Jacobian matrix with its LU decomposition
-	// ... returns condition number if known,
-	//	       0.0 if matrix is numerically singular,
-	//             -1.0 if condition number is unknown
+	// ... returns estimated reciprocal condition number if known,
+	//	       -1.0 if condition number is unknown
+	//	       ... rcond = 0.0         ==> exactly singular
+	//		   rcond < DBL_EPSILON ==> numerically singular
+	//		   rcond = 1.0         ==> orthogonal matrix
 	fp solve_linear_system(int rhs_gfn, int x_gfn,
 			       const struct linear_solver_pars& pars,
 			       bool print_msg_flag);