/*
* 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.ignite.ml.math.functions;
/**
* Compatibility with Apache Mahout.
*/
public final class Functions {
/** Function that returns {@code Math.abs(a)}. */
public static final IgniteDoubleFunction<Double> ABS = Math::abs;
/** Function that returns its argument. */
public static final IgniteDoubleFunction<Double> IDENTITY = (a) -> a;
/** Function that returns {@code Math.log(a) / Math.log(2)}. */
public static final IgniteDoubleFunction<Double> LOG2 = (a) -> Math.log(a) * 1.4426950408889634;
/** Function that returns {@code -a}. */
public static final IgniteDoubleFunction<Double> NEGATE = (a) -> -a;
/** Function that returns {@code a < 0 ? -1 : a > 0 ? 1 : 0 }. */
public static final IgniteDoubleFunction<Double> SIGN = (a) -> a < 0.0 ? -1.0 : a > 0.0 ? 1.0 : 0.0;
/** Function that returns {@code a * a}. */
public static final IgniteDoubleFunction<Double> SQUARE = (a) -> a * a;
/** Function that returns {@code 1 / (1 + exp(-a) } */
public static final IgniteDoubleFunction<Double> SIGMOID = (a) -> 1.0 / (1.0 + Math.exp(-a));
/** Function that returns {@code 1 / a } */
public static final IgniteDoubleFunction<Double> INV = (a) -> 1.0 / a;
/** Function that returns {@code a * (1-a) } */
public static final IgniteDoubleFunction<Double> SIGMOIDGRADIENT = (a) -> a * (1.0 - a);
/** Function that returns {@code a % b}. */
public static final IgniteBiFunction<Double, Double, Double> MOD = (a, b) -> a % b;
/** Function that returns {@code a * b}. */
public static final IgniteBiFunction<Double, Double, Double> MULT = (a, b) -> a * b;
/** Function that returns {@code Math.log(a) / Math.log(b)}. */
public static final IgniteBiFunction<Double, Double, Double> LG = (a, b) -> Math.log(a) / Math.log(b);
/** Function that returns {@code a + b}. */
public static final IgniteBiFunction<Double, Double, Double> PLUS = (a, b) -> a + b;
/** Function that returns {@code a - b}. */
public static final IgniteBiFunction<Double, Double, Double> MINUS = (a, b) -> a - b;
/** Function that returns {@code abs(a - b)}. */
public static final IgniteBiFunction<Double, Double, Double> MINUS_ABS = (a, b) -> Math.abs(a - b);
/** Function that returns {@code max(abs(a), abs(b))}. */
public static final IgniteBiFunction<Double, Double, Double> MAX_ABS = (a, b) -> Math.max(Math.abs(a), Math.abs(b));
/** Function that returns {@code min(abs(a), abs(b))}. */
public static final IgniteBiFunction<Double, Double, Double> MIN_ABS = (a, b) -> Math.min(Math.abs(a), Math.abs(b));
/** Function that returns {@code Math.abs(a) + Math.abs(b)}. */
public static final IgniteBiFunction<Double, Double, Double> PLUS_ABS = (a, b) -> Math.abs(a) + Math.abs(b);
/** Function that returns {@code (a - b) * (a - b)} */
public static final IgniteBiFunction<Double, Double, Double> MINUS_SQUARED = (a, b) -> (a - b) * (a - b);
/** Function that returns {@code a < b ? -1 : a > b ? 1 : 0}. */
public static final IgniteBiFunction<Double, Double, Double> COMPARE = (a, b) -> a < b ? -1.0 : a > b ? 1.0 : 0.0;
/**
* Function that returns {@code a + b}. {@code a} is a variable, {@code b} is fixed.
*
* @param b Value to add.
* @return Function for this operation.
*/
public static IgniteDoubleFunction<Double> plus(final double b) {
return (a) -> a + b;
}
/**
* Function that returns {@code a * b}. {@code a} is a variable, {@code b} is fixed.
*
* @param b Value to multiply to.
* @return Function for this operation.
*/
public static IgniteDoubleFunction<Double> mult(final double b) {
return (a) -> a * b;
}
/**
* Function that returns {@code a / b}. {@code a} is a variable, {@code b} is fixed.
*
* @param b Value to divide to.
* @return Function for this operation.
*/
public static IgniteDoubleFunction<Double> div(double b) {
return mult(1 / b);
}
/**
* Function that returns {@code a + b*constant}. {@code a} and {@code b} are variables,
* {@code constant} is fixed.
*
* @param constant Value to use in multiply.
* @return Function for this operation.
*/
public static IgniteBiFunction<Double, Double, Double> plusMult(double constant) {
return (a, b) -> a + b * constant;
}
/**
* Function that returns {@code a - b*constant}. {@code a} and {@code b} are variables,
* {@code constant} is fixed.
*
* @param constant Value to use in multiply.
* @return Function for this operation.
*/
public static IgniteBiFunction<Double, Double, Double> minusMult(double constant) {
return (a, b) -> a - b * constant;
}
/** Function that returns passed constant. */
public static IgniteDoubleFunction<Double> constant(Double c) {
return a -> c;
}
/**
* Function that returns {@code Math.pow(a, b)}.
*
* @param b Power value.
* @return Function for given power.
*/
public static IgniteDoubleFunction<Double> pow(final double b) {
return (a) -> {
if (b == 2)
return a * a;
else
return Math.pow(a, b);
};
}
}