From ba84ec24bf8bf262f7ffa232a07fe1a8f2e8ca71 Mon Sep 17 00:00:00 2001
From: andy <andy>
Date: Thu, 12 Dec 2002 02:15:06 +0000
Subject: [PATCH] Changing the thresholds to be bigger in the previous patch
 isn't really useful unless we simultaneously change the per-iteration deltas
 to be smaller.  Add another pseudo-tunable to control the speed with which we
 change values across iterations.  As it turns out, this is much more
 effective than the threshold tunable.  It does come at the cost of lower
 solution performance, however.

---
 src/FDM/YASim/Airplane.cpp | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/src/FDM/YASim/Airplane.cpp b/src/FDM/YASim/Airplane.cpp
index 05c64df31..6f3b68a07 100644
--- a/src/FDM/YASim/Airplane.cpp
+++ b/src/FDM/YASim/Airplane.cpp
@@ -15,6 +15,18 @@ namespace yasim {
 inline float norm(float f) { return f<1 ? 1/f : f; }
 inline float abs(float f) { return f<0 ? -f : f; }
 
+// Solver threshold.  How close to the solution are we trying
+// to get?  Trying too hard can result in oscillations about
+// the correct solution, which is bad.  Stick this in as a
+// compile time constant for now, and consider making it
+// settable per-model.
+const float STHRESH = 1;
+
+// How slowly do we change values in the solver.  Too slow, and
+// the solution converges very slowly.  Too fast, and it can
+// oscillate.
+const float SOLVE_TWEAK = 0.3226;
+
 Airplane::Airplane()
 {
     _emptyWeight = 0;
@@ -787,7 +799,7 @@ void Airplane::runApproach()
 
 void Airplane::applyDragFactor(float factor)
 {
-    float applied = Math::sqrt(factor);
+    float applied = Math::pow(factor, SOLVE_TWEAK);
     _dragFactor *= applied;
     _wing->setDragScale(_wing->getDragScale() * applied);
     _tail->setDragScale(_tail->getDragScale() * applied);
@@ -804,7 +816,7 @@ void Airplane::applyDragFactor(float factor)
 
 void Airplane::applyLiftRatio(float factor)
 {
-    float applied = Math::sqrt(factor);
+    float applied = Math::pow(factor, SOLVE_TWEAK);
     _liftRatio *= applied;
     _wing->setLiftRatio(_wing->getLiftRatio() * applied);
     _tail->setLiftRatio(_tail->getLiftRatio() * applied);
@@ -929,13 +941,6 @@ void Airplane::solve()
 	applyDragFactor(dragFactor);
 	applyLiftRatio(liftFactor);
 
-	// Solver threshold.  How close to the solution are we trying
-	// to get?  Trying too hard can result in oscillations about
-	// the correct solution, which is bad.  Stick this in as a
-	// compile time constant for now, and consider making it
-	// settable per-model.
-	float STHRESH = 1.6;
-
 	// DON'T do the following until the above are sane
 	if(normFactor(dragFactor) > STHRESH*1.0001
 	   || normFactor(liftFactor) > STHRESH*1.0001)
@@ -944,8 +949,8 @@ void Airplane::solve()
 	}
 
 	// OK, now we can adjust the minor variables:
-	_cruiseAoA += 0.5f*aoaDelta;
-	_tailIncidence += 0.5f*tailDelta;
+	_cruiseAoA += SOLVE_TWEAK*aoaDelta;
+	_tailIncidence += SOLVE_TWEAK*tailDelta;
 	
 	_cruiseAoA = clamp(_cruiseAoA, -0.175f, 0.175f);
 	_tailIncidence = clamp(_tailIncidence, -0.175f, 0.175f);
@@ -960,7 +965,7 @@ void Airplane::solve()
                 break;
 
             // Otherwise, adjust and do the next iteration
-            _approachElevator.val += 0.8 * elevDelta;
+            _approachElevator.val += SOLVE_TWEAK * elevDelta;
             if(abs(_approachElevator.val) > 1) {
                 _failureMsg = "Insufficient elevator to trim for approach";
                 break;
-- 
2.39.5