[mlpack-git] master: Add implementation of logisitc activation function. (a12ddcc)
gitdub at big.cc.gt.atl.ga.us
gitdub at big.cc.gt.atl.ga.us
Thu Mar 5 22:08:40 EST 2015
Repository : https://github.com/mlpack/mlpack
On branch : master
Link : https://github.com/mlpack/mlpack/compare/904762495c039e345beba14c1142fd719b3bd50e...f94823c800ad6f7266995c700b1b630d5ffdcf40
>---------------------------------------------------------------
commit a12ddccb33c6dbb9c342d6a7719cfe433b715b79
Author: Marcus Edel <marcus.edel at fu-berlin.de>
Date: Wed Dec 31 21:51:36 2014 +0100
Add implementation of logisitc activation function.
>---------------------------------------------------------------
a12ddccb33c6dbb9c342d6a7719cfe433b715b79
.../ann/activation_functions/logistic_function.hpp | 100 +++++++++++++++++++++
1 file changed, 100 insertions(+)
diff --git a/src/mlpack/methods/ann/activation_functions/logistic_function.hpp b/src/mlpack/methods/ann/activation_functions/logistic_function.hpp
new file mode 100644
index 0000000..728a2c5
--- /dev/null
+++ b/src/mlpack/methods/ann/activation_functions/logistic_function.hpp
@@ -0,0 +1,100 @@
+/**
+ * @file logistic_function.hpp
+ * @author Marcus Edel
+ *
+ * Definition and implementation of the logistic function.
+ */
+#ifndef __MLPACK_METHODS_ANN_ACTIVATION_FUNCTIONS_LOGISTIC_FUNCTION_HPP
+#define __MLPACK_METHODS_ANN_ACTIVATION_FUNCTIONS_LOGISTIC_FUNCTION_HPP
+
+#include <mlpack/core.hpp>
+
+namespace mlpack {
+namespace ann /** Artificial Neural Network. */ {
+
+/**
+ * The logistic function, defined by
+ *
+ * @f[
+ * f(x) &=& \frac{1}{1 + e^{-x}} \\
+ * f'(x) &=& f(x) * (1 - f(x))
+ * f^{-1}(y) &=& ln(\frac{y}{1-y})
+ * @f]
+ */
+class LogisticFunction
+{
+ public:
+ /**
+ * Computes the logistic function.
+ *
+ * @param x Input data.
+ * @return f(x).
+ */
+ static double fn(const double x)
+ {
+ return 1.0 / (1.0 + arma::trunc_exp(-x));
+ }
+
+ /**
+ * Computes the logistic function.
+ *
+ * @param x Input data.
+ * @param y The resulting output activation.
+ */
+ template<typename InputVecType, typename OutputVecType>
+ static void fn(const InputVecType& x, OutputVecType& y)
+ {
+ y = 1.0 / (1.0 + arma::trunc_exp(-x));
+ }
+
+ /**
+ * Computes the first derivative of the logistic function.
+ *
+ * @param x Input data.
+ * @return f'(x)
+ */
+ static double deriv(const double y)
+ {
+ return y * (1.0 - y);
+ }
+
+ /**
+ * Computes the first derivatives of the logistic function.
+ *
+ * @param y Input activations.
+ * @param x The resulting derivatives.
+ */
+ template<typename InputVecType, typename OutputVecType>
+ static void deriv(const InputVecType& y, OutputVecType& x)
+ {
+ x = y % (1.0 - y);
+ }
+
+ /**
+ * Computes the inverse of the logistic function.
+ *
+ * @param y Input data.
+ * @return f^{-1}(y)
+ */
+ static double inv(const double y)
+ {
+ return arma::trunc_log(y / (1 - y));
+ }
+
+ /**
+ * Computes the inverse of the logistic function.
+ *
+ * @param y Input data.
+ * @return x The resulting inverse of the input data.
+ */
+ template<typename InputVecType, typename OutputVecType>
+ static void inv(const InputVecType& y, OutputVecType& x)
+ {
+ x = arma::trunc_log(y / (1 - y));
+ }
+}; // class LogisticFunction
+
+}; // namespace ann
+}; // namespace mlpack
+
+#endif
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