[mlpack-svn] r13524 - mlpack/trunk/src/mlpack/core/metrics

[fastlab-svn at coffeetalk-1.cc.gatech.edu]

Author: rcurtin
Date: 2012-09-10 15:27:44 -0400 (Mon, 10 Sep 2012)
New Revision: 13524

Modified:
   mlpack/trunk/src/mlpack/core/metrics/mahalanobis_distance.hpp
   mlpack/trunk/src/mlpack/core/metrics/mahalanobis_distance_impl.hpp
Log:
Add constructor which automatically creates identity covariance, and don't check
if covariance is initialized when calling Evaluate().


Modified: mlpack/trunk/src/mlpack/core/metrics/mahalanobis_distance.hpp
===================================================================
--- mlpack/trunk/src/mlpack/core/metrics/mahalanobis_distance.hpp	2012-09-10 19:17:14 UTC (rev 13523)
+++ mlpack/trunk/src/mlpack/core/metrics/mahalanobis_distance.hpp	2012-09-10 19:27:44 UTC (rev 13524)
@@ -48,12 +48,20 @@
  public:
   /**
    * Initialize the Mahalanobis distance with the empty matrix as covariance.
-   * Because we don't actually know the size of the vectors we will be using, we
-   * delay creation of the covariance matrix until evaluation.
+   * Don't call Evaluate() until you set the covariance with Covariance()!
    */
   MahalanobisDistance() { }
 
   /**
+   * Initialize the Mahalanobis distance with the identity matrix of the given
+   * dimensionality.
+   *
+   * @param dimensionality Dimesnsionality of the covariance matrix.
+   */
+  MahalanobisDistance(const size_t dimensionality) :
+      covariance(arma::eye<arma::mat>(dimensionality, dimensionality)) { }
+
+  /**
    * Initialize the Mahalanobis distance with the given covariance matrix.  The
    * given covariance matrix will be copied (this is not optimal).
    *
@@ -63,7 +71,9 @@
 
   /**
    * Evaluate the distance between the two given points using this Mahalanobis
-   * distance.
+   * distance.  If the covariance matrix has not been set (i.e. if you used the
+   * empty constructor and did not later modify the covariance matrix), calling
+   * this method will probably result in a crash.
    *
    * @param a First vector.
    * @param b Second vector.

Modified: mlpack/trunk/src/mlpack/core/metrics/mahalanobis_distance_impl.hpp
===================================================================
--- mlpack/trunk/src/mlpack/core/metrics/mahalanobis_distance_impl.hpp	2012-09-10 19:17:14 UTC (rev 13523)
+++ mlpack/trunk/src/mlpack/core/metrics/mahalanobis_distance_impl.hpp	2012-09-10 19:27:44 UTC (rev 13524)
@@ -20,10 +20,6 @@
 double MahalanobisDistance<false>::Evaluate(const VecType1& a,
                                             const VecType2& b)
 {
-  // Check if covariance matrix has been initialized.
-  if (covariance.n_rows == 0)
-    covariance = arma::eye<arma::mat>(a.n_elem, a.n_elem);
-
   arma::vec m = (a - b);
   arma::mat out = trans(m) * covariance * m; // 1x1
   return out[0];