From 6031c99bec7fb3f5fd00c0e8d1eb49bae460f594 Mon Sep 17 00:00:00 2001
From: Jonathan Westhues <jwesthues@cq.cx>
Date: Mon, 12 May 2008 18:35:31 -0800
Subject: [PATCH] Scale columns of the Jacobian before least squares solving;
 this lets me reweight the parameters, e.g. to encourage the solver to make
 changes to the point being dragged.

[git-p4: depot-paths = "//depot/solvespace/": change = 1719]
---
 solvespace.h |  2 ++
 system.cpp   | 16 +++++++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/solvespace.h b/solvespace.h
index c8499bd..c2e5267 100644
--- a/solvespace.h
+++ b/solvespace.h
@@ -122,6 +122,8 @@ public:
             double       num[MAX_UNKNOWNS][MAX_UNKNOWNS];
         }           A;
 
+        double      scale[MAX_UNKNOWNS];
+
         // Some helpers for the least squares solve
         double AAt[MAX_UNKNOWNS][MAX_UNKNOWNS];
         double Z[MAX_UNKNOWNS];
diff --git a/system.cpp b/system.cpp
index 9c5d0ef..7f9c729 100644
--- a/system.cpp
+++ b/system.cpp
@@ -273,6 +273,20 @@ bool System::SolveLinearSystem(double X[], double A[][MAX_UNKNOWNS],
 bool System::SolveLeastSquares(void) {
     int r, c, i;
 
+    // Scale the columns; this scale weights the parameters for the least
+    // squares solve, so that we can encourage the solver to make bigger
+    // changes in some parameters, and smaller in others.
+    for(c = 0; c < mat.n; c++) {
+        if(IsDragged(mat.param[c])) {
+            mat.scale[c] = 1/5.0;
+        } else {
+            mat.scale[c] = 1;
+        }
+        for(r = 0; r < mat.m; r++) {
+            mat.A.num[r][c] *= mat.scale[c];
+        }
+    }
+
     // Write A*A'
     for(r = 0; r < mat.m; r++) {
         for(c = 0; c < mat.m; c++) {  // yes, AAt is square
@@ -292,7 +306,7 @@ bool System::SolveLeastSquares(void) {
         for(i = 0; i < mat.m; i++) {
             sum += mat.A.num[i][c]*mat.Z[i];
         }
-        mat.X[c] = sum;
+        mat.X[c] = sum * mat.scale[c];
     }
     return true;
 }