From 267b86ec1412a1b9cfffce639237ea26838b24fb Mon Sep 17 00:00:00 2001
From: cbeall3 <cbeall3@gatech.edu>
Date: Sat, 3 May 2014 11:54:01 -0400
Subject: [PATCH] Remove svd inverse_square_root

---
 gtsam/base/Matrix.cpp | 22 ----------------------
 gtsam/base/Matrix.h   |  2 +-
 2 files changed, 1 insertion(+), 23 deletions(-)

diff --git a/gtsam/base/Matrix.cpp b/gtsam/base/Matrix.cpp
index 3b16beb51..92c9a525e 100644
--- a/gtsam/base/Matrix.cpp
+++ b/gtsam/base/Matrix.cpp
@@ -642,29 +642,7 @@ Matrix cholesky_inverse(const Matrix &A)
 //  return BNU::prod(trans(inv), inv);
 }
 
-#if 0
 /* ************************************************************************* */
-// TODO, would be faster with Cholesky
-Matrix inverse_square_root(const Matrix& A) {
-  size_t m = A.cols(), n = A.rows();
-  if (m!=n)
-    throw invalid_argument("inverse_square_root: A must be square");
-
-  // Perform SVD, TODO: symmetric SVD?
-  Matrix U,V;
-  Vector S;
-  svd(A,U,S,V);
-
-  // invert and sqrt diagonal of S
-  // We also arbitrarily choose sign to make result have positive signs
-  for(size_t i = 0; i<m; i++) S(i) = - pow(S(i),-0.5);
-  return vector_scale(S, V); // V*S;
-}
-#endif
-
-/* ************************************************************************* */
-// New, improved, with 100% more Cholesky goodness!
-//
 // Semantics: 
 // if B = inverse_square_root(A), then all of the following are true:
 // inv(B) * inv(B)' == A
diff --git a/gtsam/base/Matrix.h b/gtsam/base/Matrix.h
index caee66851..6386bd526 100644
--- a/gtsam/base/Matrix.h
+++ b/gtsam/base/Matrix.h
@@ -418,7 +418,7 @@ GTSAM_EXPORT Matrix3 skewSymmetric(double wx, double wy, double wz);
 template<class Derived>
 inline Matrix3 skewSymmetric(const Eigen::MatrixBase<Derived>& w) { return skewSymmetric(w(0),w(1),w(2));}
 
-/** Use SVD to calculate inverse square root of a matrix */
+/** Use Cholesky to calculate inverse square root of a matrix */
 GTSAM_EXPORT Matrix inverse_square_root(const Matrix& A);
 
 /** Calculate the LL^t decomposition of a S.P.D matrix */