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/*
 * 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.commons.math3.analysis.differentiation;

import java.io.Serializable;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.math3.Field;
import org.apache.commons.math3.FieldElement;
import org.apache.commons.math3.RealFieldElement;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.util.FastMath;
import org.apache.commons.math3.util.MathArrays;
import org.apache.commons.math3.util.MathUtils;
import org.apache.commons.math3.util.Precision;

/**
 * First derivative computation with large number of variables.
 * 

* This class plays a similar role to {@link DerivativeStructure}, with * a focus on efficiency when dealing with large number of independent variables * and most computation depend only on a few of them, and when only first derivative * is desired. When these conditions are met, this class should be much faster than * {@link DerivativeStructure} and use less memory. *

* * @since 3.3 */ public class SparseGradient implements RealFieldElement, Serializable { /** Serializable UID. */ private static final long serialVersionUID = 20131025L; /** Value of the calculation. */ private double value; /** Stored derivative, each key representing a different independent variable. */ private final Map derivatives; /** Internal constructor. * @param value value of the function * @param derivatives derivatives map, a deep copy will be performed, * so the map given here will remain safe from changes in the new instance, * may be null to create an empty derivatives map, i.e. a constant value */ private SparseGradient(final double value, final Map derivatives) { this.value = value; this.derivatives = new HashMap(); if (derivatives != null) { this.derivatives.putAll(derivatives); } } /** Internal constructor. * @param value value of the function * @param scale scaling factor to apply to all derivatives * @param derivatives derivatives map, a deep copy will be performed, * so the map given here will remain safe from changes in the new instance, * may be null to create an empty derivatives map, i.e. a constant value */ private SparseGradient(final double value, final double scale, final Map derivatives) { this.value = value; this.derivatives = new HashMap(); if (derivatives != null) { for (final Map.Entry entry : derivatives.entrySet()) { this.derivatives.put(entry.getKey(), scale * entry.getValue()); } } } /** Factory method creating a constant. * @param value value of the constant * @return a new instance */ public static SparseGradient createConstant(final double value) { return new SparseGradient(value, Collections. emptyMap()); } /** Factory method creating an independent variable. * @param idx index of the variable * @param value value of the variable * @return a new instance */ public static SparseGradient createVariable(final int idx, final double value) { return new SparseGradient(value, Collections.singletonMap(idx, 1.0)); } /** * Find the number of variables. * @return number of variables */ public int numVars() { return derivatives.size(); } /** * Get the derivative with respect to a particular index variable. * * @param index index to differentiate with. * @return derivative with respect to a particular index variable */ public double getDerivative(final int index) { final Double out = derivatives.get(index); return (out == null) ? 0.0 : out; } /** * Get the value of the function. * @return value of the function. */ public double getValue() { return value; } /** {@inheritDoc} */ public double getReal() { return value; } /** {@inheritDoc} */ public SparseGradient add(final SparseGradient a) { final SparseGradient out = new SparseGradient(value + a.value, derivatives); for (Map.Entry entry : a.derivatives.entrySet()) { final int id = entry.getKey(); final Double old = out.derivatives.get(id); if (old == null) { out.derivatives.put(id, entry.getValue()); } else { out.derivatives.put(id, old + entry.getValue()); } } return out; } /** * Add in place. *

* This method is designed to be faster when used multiple times in a loop. *

*

* The instance is changed here, in order to not change the * instance the {@link #add(SparseGradient)} method should * be used. *

* @param a instance to add */ public void addInPlace(final SparseGradient a) { value += a.value; for (final Map.Entry entry : a.derivatives.entrySet()) { final int id = entry.getKey(); final Double old = derivatives.get(id); if (old == null) { derivatives.put(id, entry.getValue()); } else { derivatives.put(id, old + entry.getValue()); } } } /** {@inheritDoc} */ public SparseGradient add(final double c) { final SparseGradient out = new SparseGradient(value + c, derivatives); return out; } /** {@inheritDoc} */ public SparseGradient subtract(final SparseGradient a) { final SparseGradient out = new SparseGradient(value - a.value, derivatives); for (Map.Entry entry : a.derivatives.entrySet()) { final int id = entry.getKey(); final Double old = out.derivatives.get(id); if (old == null) { out.derivatives.put(id, -entry.getValue()); } else { out.derivatives.put(id, old - entry.getValue()); } } return out; } /** {@inheritDoc} */ public SparseGradient subtract(double c) { return new SparseGradient(value - c, derivatives); } /** {@inheritDoc} */ public SparseGradient multiply(final SparseGradient a) { final SparseGradient out = new SparseGradient(value * a.value, Collections. emptyMap()); // Derivatives. for (Map.Entry entry : derivatives.entrySet()) { out.derivatives.put(entry.getKey(), a.value * entry.getValue()); } for (Map.Entry entry : a.derivatives.entrySet()) { final int id = entry.getKey(); final Double old = out.derivatives.get(id); if (old == null) { out.derivatives.put(id, value * entry.getValue()); } else { out.derivatives.put(id, old + value * entry.getValue()); } } return out; } /** * Multiply in place. *

* This method is designed to be faster when used multiple times in a loop. *

*

* The instance is changed here, in order to not change the * instance the {@link #add(SparseGradient)} method should * be used. *

* @param a instance to multiply */ public void multiplyInPlace(final SparseGradient a) { // Derivatives. for (Map.Entry entry : derivatives.entrySet()) { derivatives.put(entry.getKey(), a.value * entry.getValue()); } for (Map.Entry entry : a.derivatives.entrySet()) { final int id = entry.getKey(); final Double old = derivatives.get(id); if (old == null) { derivatives.put(id, value * entry.getValue()); } else { derivatives.put(id, old + value * entry.getValue()); } } value *= a.value; } /** {@inheritDoc} */ public SparseGradient multiply(final double c) { return new SparseGradient(value * c, c, derivatives); } /** {@inheritDoc} */ public SparseGradient multiply(final int n) { return new SparseGradient(value * n, n, derivatives); } /** {@inheritDoc} */ public SparseGradient divide(final SparseGradient a) { final SparseGradient out = new SparseGradient(value / a.value, Collections. emptyMap()); // Derivatives. for (Map.Entry entry : derivatives.entrySet()) { out.derivatives.put(entry.getKey(), entry.getValue() / a.value); } for (Map.Entry entry : a.derivatives.entrySet()) { final int id = entry.getKey(); final Double old = out.derivatives.get(id); if (old == null) { out.derivatives.put(id, -out.value / a.value * entry.getValue()); } else { out.derivatives.put(id, old - out.value / a.value * entry.getValue()); } } return out; } /** {@inheritDoc} */ public SparseGradient divide(final double c) { return new SparseGradient(value / c, 1.0 / c, derivatives); } /** {@inheritDoc} */ public SparseGradient negate() { return new SparseGradient(-value, -1.0, derivatives); } /** {@inheritDoc} */ public Field getField() { return new Field() { /** {@inheritDoc} */ public SparseGradient getZero() { return createConstant(0); } /** {@inheritDoc} */ public SparseGradient getOne() { return createConstant(1); } /** {@inheritDoc} */ public Class> getRuntimeClass() { return SparseGradient.class; } }; } /** {@inheritDoc} */ public SparseGradient remainder(final double a) { return new SparseGradient(FastMath.IEEEremainder(value, a), derivatives); } /** {@inheritDoc} */ public SparseGradient remainder(final SparseGradient a) { // compute k such that lhs % rhs = lhs - k rhs final double rem = FastMath.IEEEremainder(value, a.value); final double k = FastMath.rint((value - rem) / a.value); return subtract(a.multiply(k)); } /** {@inheritDoc} */ public SparseGradient abs() { if (Double.doubleToLongBits(value) < 0) { // we use the bits representation to also handle -0.0 return negate(); } else { return this; } } /** {@inheritDoc} */ public SparseGradient ceil() { return createConstant(FastMath.ceil(value)); } /** {@inheritDoc} */ public SparseGradient floor() { return createConstant(FastMath.floor(value)); } /** {@inheritDoc} */ public SparseGradient rint() { return createConstant(FastMath.rint(value)); } /** {@inheritDoc} */ public long round() { return FastMath.round(value); } /** {@inheritDoc} */ public SparseGradient signum() { return createConstant(FastMath.signum(value)); } /** {@inheritDoc} */ public SparseGradient copySign(final SparseGradient sign) { final long m = Double.doubleToLongBits(value); final long s = Double.doubleToLongBits(sign.value); if ((m >= 0 && s >= 0) || (m < 0 && s < 0)) { // Sign is currently OK return this; } return negate(); // flip sign } /** {@inheritDoc} */ public SparseGradient copySign(final double sign) { final long m = Double.doubleToLongBits(value); final long s = Double.doubleToLongBits(sign); if ((m >= 0 && s >= 0) || (m < 0 && s < 0)) { // Sign is currently OK return this; } return negate(); // flip sign } /** {@inheritDoc} */ public SparseGradient scalb(final int n) { final SparseGradient out = new SparseGradient(FastMath.scalb(value, n), Collections. emptyMap()); for (Map.Entry entry : derivatives.entrySet()) { out.derivatives.put(entry.getKey(), FastMath.scalb(entry.getValue(), n)); } return out; } /** {@inheritDoc} */ public SparseGradient hypot(final SparseGradient y) { if (Double.isInfinite(value) || Double.isInfinite(y.value)) { return createConstant(Double.POSITIVE_INFINITY); } else if (Double.isNaN(value) || Double.isNaN(y.value)) { return createConstant(Double.NaN); } else { final int expX = FastMath.getExponent(value); final int expY = FastMath.getExponent(y.value); if (expX > expY + 27) { // y is negligible with respect to x return abs(); } else if (expY > expX + 27) { // x is negligible with respect to y return y.abs(); } else { // find an intermediate scale to avoid both overflow and underflow final int middleExp = (expX + expY) / 2; // scale parameters without losing precision final SparseGradient scaledX = scalb(-middleExp); final SparseGradient scaledY = y.scalb(-middleExp); // compute scaled hypotenuse final SparseGradient scaledH = scaledX.multiply(scaledX).add(scaledY.multiply(scaledY)).sqrt(); // remove scaling return scaledH.scalb(middleExp); } } } /** * Returns the hypotenuse of a triangle with sides {@code x} and {@code y} * - sqrt(x2 +y2) * avoiding intermediate overflow or underflow. * *
    *
  • If either argument is infinite, then the result is positive infinity.
  • *
  • else, if either argument is NaN then the result is NaN.
  • *
* * @param x a value * @param y a value * @return sqrt(x2 +y2) */ public static SparseGradient hypot(final SparseGradient x, final SparseGradient y) { return x.hypot(y); } /** {@inheritDoc} */ public SparseGradient reciprocal() { return new SparseGradient(1.0 / value, -1.0 / (value * value), derivatives); } /** {@inheritDoc} */ public SparseGradient sqrt() { final double sqrt = FastMath.sqrt(value); return new SparseGradient(sqrt, 0.5 / sqrt, derivatives); } /** {@inheritDoc} */ public SparseGradient cbrt() { final double cbrt = FastMath.cbrt(value); return new SparseGradient(cbrt, 1.0 / (3 * cbrt * cbrt), derivatives); } /** {@inheritDoc} */ public SparseGradient rootN(final int n) { if (n == 2) { return sqrt(); } else if (n == 3) { return cbrt(); } else { final double root = FastMath.pow(value, 1.0 / n); return new SparseGradient(root, 1.0 / (n * FastMath.pow(root, n - 1)), derivatives); } } /** {@inheritDoc} */ public SparseGradient pow(final double p) { return new SparseGradient(FastMath.pow(value, p), p * FastMath.pow(value, p - 1), derivatives); } /** {@inheritDoc} */ public SparseGradient pow(final int n) { if (n == 0) { return getField().getOne(); } else { final double valueNm1 = FastMath.pow(value, n - 1); return new SparseGradient(value * valueNm1, n * valueNm1, derivatives); } } /** {@inheritDoc} */ public SparseGradient pow(final SparseGradient e) { return log().multiply(e).exp(); } /** Compute ax where a is a double and x a {@link SparseGradient} * @param a number to exponentiate * @param x power to apply * @return ax */ public static SparseGradient pow(final double a, final SparseGradient x) { if (a == 0) { if (x.value == 0) { return x.compose(1.0, Double.NEGATIVE_INFINITY); } else if (x.value < 0) { return x.compose(Double.NaN, Double.NaN); } else { return x.getField().getZero(); } } else { final double ax = FastMath.pow(a, x.value); return new SparseGradient(ax, ax * FastMath.log(a), x.derivatives); } } /** {@inheritDoc} */ public SparseGradient exp() { final double e = FastMath.exp(value); return new SparseGradient(e, e, derivatives); } /** {@inheritDoc} */ public SparseGradient expm1() { return new SparseGradient(FastMath.expm1(value), FastMath.exp(value), derivatives); } /** {@inheritDoc} */ public SparseGradient log() { return new SparseGradient(FastMath.log(value), 1.0 / value, derivatives); } /** Base 10 logarithm. * @return base 10 logarithm of the instance */ public SparseGradient log10() { return new SparseGradient(FastMath.log10(value), 1.0 / (FastMath.log(10.0) * value), derivatives); } /** {@inheritDoc} */ public SparseGradient log1p() { return new SparseGradient(FastMath.log1p(value), 1.0 / (1.0 + value), derivatives); } /** {@inheritDoc} */ public SparseGradient cos() { return new SparseGradient(FastMath.cos(value), -FastMath.sin(value), derivatives); } /** {@inheritDoc} */ public SparseGradient sin() { return new SparseGradient(FastMath.sin(value), FastMath.cos(value), derivatives); } /** {@inheritDoc} */ public SparseGradient tan() { final double t = FastMath.tan(value); return new SparseGradient(t, 1 + t * t, derivatives); } /** {@inheritDoc} */ public SparseGradient acos() { return new SparseGradient(FastMath.acos(value), -1.0 / FastMath.sqrt(1 - value * value), derivatives); } /** {@inheritDoc} */ public SparseGradient asin() { return new SparseGradient(FastMath.asin(value), 1.0 / FastMath.sqrt(1 - value * value), derivatives); } /** {@inheritDoc} */ public SparseGradient atan() { return new SparseGradient(FastMath.atan(value), 1.0 / (1 + value * value), derivatives); } /** {@inheritDoc} */ public SparseGradient atan2(final SparseGradient x) { // compute r = sqrt(x^2+y^2) final SparseGradient r = multiply(this).add(x.multiply(x)).sqrt(); final SparseGradient a; if (x.value >= 0) { // compute atan2(y, x) = 2 atan(y / (r + x)) a = divide(r.add(x)).atan().multiply(2); } else { // compute atan2(y, x) = +/- pi - 2 atan(y / (r - x)) final SparseGradient tmp = divide(r.subtract(x)).atan().multiply(-2); a = tmp.add(tmp.value <= 0 ? -FastMath.PI : FastMath.PI); } // fix value to take special cases (+0/+0, +0/-0, -0/+0, -0/-0, +/-infinity) correctly a.value = FastMath.atan2(value, x.value); return a; } /** Two arguments arc tangent operation. * @param y first argument of the arc tangent * @param x second argument of the arc tangent * @return atan2(y, x) */ public static SparseGradient atan2(final SparseGradient y, final SparseGradient x) { return y.atan2(x); } /** {@inheritDoc} */ public SparseGradient cosh() { return new SparseGradient(FastMath.cosh(value), FastMath.sinh(value), derivatives); } /** {@inheritDoc} */ public SparseGradient sinh() { return new SparseGradient(FastMath.sinh(value), FastMath.cosh(value), derivatives); } /** {@inheritDoc} */ public SparseGradient tanh() { final double t = FastMath.tanh(value); return new SparseGradient(t, 1 - t * t, derivatives); } /** {@inheritDoc} */ public SparseGradient acosh() { return new SparseGradient(FastMath.acosh(value), 1.0 / FastMath.sqrt(value * value - 1.0), derivatives); } /** {@inheritDoc} */ public SparseGradient asinh() { return new SparseGradient(FastMath.asinh(value), 1.0 / FastMath.sqrt(value * value + 1.0), derivatives); } /** {@inheritDoc} */ public SparseGradient atanh() { return new SparseGradient(FastMath.atanh(value), 1.0 / (1.0 - value * value), derivatives); } /** Convert radians to degrees, with error of less than 0.5 ULP * @return instance converted into degrees */ public SparseGradient toDegrees() { return new SparseGradient(FastMath.toDegrees(value), FastMath.toDegrees(1.0), derivatives); } /** Convert degrees to radians, with error of less than 0.5 ULP * @return instance converted into radians */ public SparseGradient toRadians() { return new SparseGradient(FastMath.toRadians(value), FastMath.toRadians(1.0), derivatives); } /** Evaluate Taylor expansion of a sparse gradient. * @param delta parameters offsets (Δx, Δy, ...) * @return value of the Taylor expansion at x + Δx, y + Δy, ... */ public double taylor(final double ... delta) { double y = value; for (int i = 0; i < delta.length; ++i) { y += delta[i] * getDerivative(i); } return y; } /** Compute composition of the instance by a univariate function. * @param f0 value of the function at (i.e. f({@link #getValue()})) * @param f1 first derivative of the function at * the current point (i.e. f'({@link #getValue()})) * @return f(this) */ public SparseGradient compose(final double f0, final double f1) { return new SparseGradient(f0, f1, derivatives); } /** {@inheritDoc} */ public SparseGradient linearCombination(final SparseGradient[] a, final SparseGradient[] b) throws DimensionMismatchException { // compute a simple value, with all partial derivatives SparseGradient out = a[0].getField().getZero(); for (int i = 0; i < a.length; ++i) { out = out.add(a[i].multiply(b[i])); } // recompute an accurate value, taking care of cancellations final double[] aDouble = new double[a.length]; for (int i = 0; i < a.length; ++i) { aDouble[i] = a[i].getValue(); } final double[] bDouble = new double[b.length]; for (int i = 0; i < b.length; ++i) { bDouble[i] = b[i].getValue(); } out.value = MathArrays.linearCombination(aDouble, bDouble); return out; } /** {@inheritDoc} */ public SparseGradient linearCombination(final double[] a, final SparseGradient[] b) { // compute a simple value, with all partial derivatives SparseGradient out = b[0].getField().getZero(); for (int i = 0; i < a.length; ++i) { out = out.add(b[i].multiply(a[i])); } // recompute an accurate value, taking care of cancellations final double[] bDouble = new double[b.length]; for (int i = 0; i < b.length; ++i) { bDouble[i] = b[i].getValue(); } out.value = MathArrays.linearCombination(a, bDouble); return out; } /** {@inheritDoc} */ public SparseGradient linearCombination(final SparseGradient a1, final SparseGradient b1, final SparseGradient a2, final SparseGradient b2) { // compute a simple value, with all partial derivatives SparseGradient out = a1.multiply(b1).add(a2.multiply(b2)); // recompute an accurate value, taking care of cancellations out.value = MathArrays.linearCombination(a1.value, b1.value, a2.value, b2.value); return out; } /** {@inheritDoc} */ public SparseGradient linearCombination(final double a1, final SparseGradient b1, final double a2, final SparseGradient b2) { // compute a simple value, with all partial derivatives SparseGradient out = b1.multiply(a1).add(b2.multiply(a2)); // recompute an accurate value, taking care of cancellations out.value = MathArrays.linearCombination(a1, b1.value, a2, b2.value); return out; } /** {@inheritDoc} */ public SparseGradient linearCombination(final SparseGradient a1, final SparseGradient b1, final SparseGradient a2, final SparseGradient b2, final SparseGradient a3, final SparseGradient b3) { // compute a simple value, with all partial derivatives SparseGradient out = a1.multiply(b1).add(a2.multiply(b2)).add(a3.multiply(b3)); // recompute an accurate value, taking care of cancellations out.value = MathArrays.linearCombination(a1.value, b1.value, a2.value, b2.value, a3.value, b3.value); return out; } /** {@inheritDoc} */ public SparseGradient linearCombination(final double a1, final SparseGradient b1, final double a2, final SparseGradient b2, final double a3, final SparseGradient b3) { // compute a simple value, with all partial derivatives SparseGradient out = b1.multiply(a1).add(b2.multiply(a2)).add(b3.multiply(a3)); // recompute an accurate value, taking care of cancellations out.value = MathArrays.linearCombination(a1, b1.value, a2, b2.value, a3, b3.value); return out; } /** {@inheritDoc} */ public SparseGradient linearCombination(final SparseGradient a1, final SparseGradient b1, final SparseGradient a2, final SparseGradient b2, final SparseGradient a3, final SparseGradient b3, final SparseGradient a4, final SparseGradient b4) { // compute a simple value, with all partial derivatives SparseGradient out = a1.multiply(b1).add(a2.multiply(b2)).add(a3.multiply(b3)).add(a4.multiply(b4)); // recompute an accurate value, taking care of cancellations out.value = MathArrays.linearCombination(a1.value, b1.value, a2.value, b2.value, a3.value, b3.value, a4.value, b4.value); return out; } /** {@inheritDoc} */ public SparseGradient linearCombination(final double a1, final SparseGradient b1, final double a2, final SparseGradient b2, final double a3, final SparseGradient b3, final double a4, final SparseGradient b4) { // compute a simple value, with all partial derivatives SparseGradient out = b1.multiply(a1).add(b2.multiply(a2)).add(b3.multiply(a3)).add(b4.multiply(a4)); // recompute an accurate value, taking care of cancellations out.value = MathArrays.linearCombination(a1, b1.value, a2, b2.value, a3, b3.value, a4, b4.value); return out; } /** * Test for the equality of two sparse gradients. *

* Sparse gradients are considered equal if they have the same value * and the same derivatives. *

* @param other Object to test for equality to this * @return true if two sparse gradients are equal */ @Override public boolean equals(Object other) { if (this == other) { return true; } if (other instanceof SparseGradient) { final SparseGradient rhs = (SparseGradient)other; if (!Precision.equals(value, rhs.value, 1)) { return false; } if (derivatives.size() != rhs.derivatives.size()) { return false; } for (final Map.Entry entry : derivatives.entrySet()) { if (!rhs.derivatives.containsKey(entry.getKey())) { return false; } if (!Precision.equals(entry.getValue(), rhs.derivatives.get(entry.getKey()), 1)) { return false; } } return true; } return false; } /** * Get a hashCode for the derivative structure. * @return a hash code value for this object * @since 3.2 */ @Override public int hashCode() { return 743 + 809 * MathUtils.hash(value) + 167 * derivatives.hashCode(); } }




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