From efe17860dbafcb0a4ce0ada799b00afa80097b3c Mon Sep 17 00:00:00 2001
From: Oliver Sander <sander@igpm.rwth-aachen.de>
Date: Thu, 11 Feb 2010 22:02:36 +0000
Subject: [PATCH] implement derivativeOfDistanceSquaredWRTSecondArgument().
Not tested yet
[[Imported from SVN: r5549]]
---
src/unitvector.hh | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/src/unitvector.hh b/src/unitvector.hh
index 9826c247..ba3321fc 100644
--- a/src/unitvector.hh
+++ b/src/unitvector.hh
@@ -32,6 +32,16 @@ public:
return std::acos(a.data_ * b.data_);
}
+ /** \brief Compute the gradient of the squared distance function keeping the first argument fixed
+
+ Unlike the distance itself the squared distance is differentiable at zero
+ */
+ static EmbeddedTangentVector derivativeOfDistanceSquaredWRTSecondArgument(const UnitVector& a, const UnitVector& b) {
+ EmbeddedTangentVector result = a.data_;
+ result *= -2*std::acos(a.data_ * b.data_) / std::sqrt(1-(a.data_*b.data_)*(a.data_*b.data_));
+ return result;
+ }
+
/** \brief Write LocalKey object to output stream */
friend std::ostream& operator<< (std::ostream& s, const UnitVector& unitVector)
{
--
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