[mlpack-svn] r10923 - mlpack/trunk/src/mlpack/core/kernels
fastlab-svn at coffeetalk-1.cc.gatech.edu
fastlab-svn at coffeetalk-1.cc.gatech.edu
Wed Dec 21 14:24:10 EST 2011
Author: ajinkya
Date: 2011-12-21 14:24:09 -0500 (Wed, 21 Dec 2011)
New Revision: 10923
Added:
mlpack/trunk/src/mlpack/core/kernels/laplacian_kernel.hpp
Modified:
mlpack/trunk/src/mlpack/core/kernels/CMakeLists.txt
Log:
laplacian kernel
Modified: mlpack/trunk/src/mlpack/core/kernels/CMakeLists.txt
===================================================================
--- mlpack/trunk/src/mlpack/core/kernels/CMakeLists.txt 2011-12-21 19:17:38 UTC (rev 10922)
+++ mlpack/trunk/src/mlpack/core/kernels/CMakeLists.txt 2011-12-21 19:24:09 UTC (rev 10923)
@@ -8,6 +8,7 @@
cosine_distance.hpp
cosine_distance_impl.hpp
exponential_kernel.hpp
+ laplacian_kernel.hpp
)
# add directory name to sources
Added: mlpack/trunk/src/mlpack/core/kernels/laplacian_kernel.hpp
===================================================================
--- mlpack/trunk/src/mlpack/core/kernels/laplacian_kernel.hpp (rev 0)
+++ mlpack/trunk/src/mlpack/core/kernels/laplacian_kernel.hpp 2011-12-21 19:24:09 UTC (rev 10923)
@@ -0,0 +1,92 @@
+/**
+ * @file laplacian_kernel.hpp
+ * @author Ajinkya Kale <kaleajinkya at gmail.com>
+ *
+ * Implementation of the Laplacian kernel (LaplacianKernel).
+ */
+#ifndef __MLPACK_CORE_KERNELS_LAPLACIAN_KERNEL_HPP
+#define __MLPACK_CORE_KERNELS_LAPLACIAN_KERNEL_HPP
+
+#include <mlpack/core.hpp>
+
+namespace mlpack {
+namespace kernel {
+
+/**
+ * The standard Laplacian kernel. Given two vectors @f$ x @f$, @f$ y @f$, and a
+ * bandwidth @f$ \mu @f$ (set in the constructor),
+ *
+ * @f[
+ * K(x, y) = \exp(-\frac{|| x - y ||}{ \mu}).
+ * @f]
+ *
+ * The implementation is all in the header file because it is so simple.
+ */
+class LaplacianKernel
+{
+ public:
+ /**
+ * Default constructor; sets bandwidth to 1.0.
+ */
+ LaplacianKernel() : bandwidth(1.0), gamma(-1.0)
+ { }
+
+ /**
+ * Construct the Laplacian kernel with a custom bandwidth.
+ *
+ * @param bandwidth The bandwidth of the kernel (@f$\mu at f$).
+ */
+ LaplacianKernel(double bandwidth) :
+ bandwidth(bandwidth),
+ gamma(-pow(bandwidth, -1.0))
+ { }
+
+ /**
+ * Evaluation of the Laplacian kernel. This could be generalized to use any
+ * distance metric, not the Euclidean distance, but for now, the Euclidean
+ * distance is used.
+ *
+ * @tparam VecType Type of vector (likely arma::vec or arma::spvec).
+ * @param a First vector.
+ * @param b Second vector.
+ * @return K(a, b) using the bandwidth (@f$\mu at f$) specified in the
+ * constructor.
+ */
+ template<typename VecType>
+ double Evaluate(const VecType& a, const VecType& b) const
+ {
+ // The precalculation of gamma saves us a little computation time.
+ return exp(gamma * sqrt(metric::SquaredEuclideanDistance::Evaluate(a, b)));
+ }
+
+ /**
+ * Evaluation of the Laplacian kernel using a double precision argument.
+ *
+ * @param t double value.
+ * @return K(t) using the bandwidth (@f$\mu at f$) specified in the
+ * constructor.
+ */
+ double Evaluate(double t) const
+ {
+ // The precalculation of gamma saves us a little computation time.
+ return exp(gamma * t);
+ }
+
+ //! Get the bandwidth.
+ const double& Bandwidth() const { return bandwidth; }
+ //! Get the precalculated constant.
+ const double& Gamma() const { return gamma; }
+
+ private:
+ //! Kernel bandwidth.
+ double bandwidth;
+
+ //! Precalculated constant depending on the bandwidth;
+ //! @f$ \gamma = -\frac{1}{ \mu} @f$.
+ double gamma;
+};
+
+}; // namespace kernel
+}; // namespace mlpack
+
+#endif
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