| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.spark.mllib.clustering |
| |
| import breeze.linalg.{max, sum, DenseMatrix => BDM, DenseVector => BDV} |
| import breeze.numerics._ |
| |
| /** |
| * Utility methods for LDA. |
| */ |
| private[clustering] object LDAUtils { |
| /** |
| * Log Sum Exp with overflow protection using the identity: |
| * For any a: $\log \sum_{n=1}^N \exp\{x_n\} = a + \log \sum_{n=1}^N \exp\{x_n - a\}$ |
| */ |
| private[clustering] def logSumExp(x: BDV[Double]): Double = { |
| val a = max(x) |
| a + log(sum(exp(x :- a))) |
| } |
| |
| /** |
| * For theta ~ Dir(alpha), computes E[log(theta)] given alpha. Currently the implementation |
| * uses [[breeze.numerics.digamma]] which is accurate but expensive. |
| */ |
| private[clustering] def dirichletExpectation(alpha: BDV[Double]): BDV[Double] = { |
| digamma(alpha) - digamma(sum(alpha)) |
| } |
| |
| /** |
| * Computes [[dirichletExpectation()]] row-wise, assuming each row of alpha are |
| * Dirichlet parameters. |
| */ |
| private[clustering] def dirichletExpectation(alpha: BDM[Double]): BDM[Double] = { |
| val rowSum = sum(alpha(breeze.linalg.*, ::)) |
| val digAlpha = digamma(alpha) |
| val digRowSum = digamma(rowSum) |
| val result = digAlpha(::, breeze.linalg.*) - digRowSum |
| result |
| } |
| |
| } |