From 6c50e510a5fcadab19a6d5ff709c0da473e4ace0 Mon Sep 17 00:00:00 2001
From: Lorenz Meier <lm@inf.ethz.ch>
Date: Fri, 18 Jul 2014 07:28:49 +0200
Subject: Derivative fix: Comments and code style

---
 src/modules/controllib/blocks.cpp | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

(limited to 'src/modules/controllib/blocks.cpp')

diff --git a/src/modules/controllib/blocks.cpp b/src/modules/controllib/blocks.cpp
index 04cb023a8..0175acda9 100644
--- a/src/modules/controllib/blocks.cpp
+++ b/src/modules/controllib/blocks.cpp
@@ -293,10 +293,16 @@ int blockIntegralTrapTest()
 
 float BlockDerivative::update(float input)
 {
-	float output = 0.0f;
+	float output;
 	if (_initialized) {
 		output = _lowPass.update((input - getU()) / getDt());
 	} else {
+		// if this is the first call to update
+		// we have no valid derivative
+		// and so we use the assumption the
+		// input value is not changing much,
+		// which is the best we can do here.
+		output = 0.0f;
 		_initialized = true;
 	}
 	setU(input);
-- 
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