From 628cef3d97103a7a7348f66c1a9f6a7680b64443 Mon Sep 17 00:00:00 2001
From: couriersud <couriersud@arcor.de>
Date: Mon, 28 Mar 2016 13:45:45 +0200
Subject: [PATCH] Added some notes about Sherman-Morrison.

---
 nl_examples/kidniki.c              |  4 ++--
 src/lib/netlist/solver/nld_ms_sm.h | 25 +++++++++++++++++++++++++
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/nl_examples/kidniki.c b/nl_examples/kidniki.c
index 263e0d3eb7d..603d2064f8d 100644
--- a/nl_examples/kidniki.c
+++ b/nl_examples/kidniki.c
@@ -14,8 +14,8 @@ NETLIST_START(dummy)
 	PARAM(Solver.NR_LOOPS, 300)
 	PARAM(Solver.GS_LOOPS, 1)
 	PARAM(Solver.GS_THRESHOLD, 6)
-	PARAM(Solver.ITERATIVE, "SM")
-	//PARAM(Solver.ITERATIVE, "MAT")
+	//PARAM(Solver.ITERATIVE, "SM")
+	PARAM(Solver.ITERATIVE, "MAT")
 	//PARAM(Solver.ITERATIVE, "GMRES")
 	//PARAM(Solver.ITERATIVE, "SOR")
 	PARAM(Solver.DYNAMIC_TS, 0)
diff --git a/src/lib/netlist/solver/nld_ms_sm.h b/src/lib/netlist/solver/nld_ms_sm.h
index 81395a11492..7336e060510 100644
--- a/src/lib/netlist/solver/nld_ms_sm.h
+++ b/src/lib/netlist/solver/nld_ms_sm.h
@@ -3,6 +3,31 @@
 /*
  * nld_ms_direct.h
  *
+ *
+ * Sherman-Morrison Solver
+ *
+ * Computes the updated inverse of A given that the change in A is
+ *
+ * A <- A + (u x v)   u,v vectors
+ *
+ * In this specific implementation, u is a unit vector specifying the row which
+ * changed. Thus v contains the changed column.
+ *
+ * Than z = A⁻¹ u ,  w = transpose(A⁻¹) v , lambda = v z
+ *
+ * A⁻¹ <- 1.0 / (1.0 + lambda) * (z x w)
+ *
+ * The approach is iterative and applied for each row changed.
+ *
+ * The performance for a typical circuit like kidniki compared to Gaussian
+ * elimination is poor:
+ *
+ * a) The code needs to be run for each row change.
+ * b) The inverse of A typically is fully occupied.
+ *
+ * It may have advantages for circuits with a high number of elements and only
+ * few dynamic/active components.
+ *
  */
 
 #ifndef NLD_MS_SM_H_