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oj! Algorithms - ojAlgo - is Open Source Java code that has to do with mathematics, linear algebra and optimisation.
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/*
 * Copyright 1997-2021 Optimatika
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package org.ojalgo.function.multiary;

import org.ojalgo.matrix.store.GenericStore;
import org.ojalgo.matrix.store.MatrixStore;
import org.ojalgo.matrix.store.PhysicalStore;
import org.ojalgo.matrix.store.PhysicalStore.Factory;
import org.ojalgo.matrix.store.Primitive64Store;
import org.ojalgo.scalar.ComplexNumber;
import org.ojalgo.scalar.RationalNumber;
import org.ojalgo.scalar.Scalar;
import org.ojalgo.structure.Access1D;
import org.ojalgo.structure.Access2D;

/**
 * [x]^T[Q][x] + c
 *
 * @author apete
 */
public final class PureQuadraticFunction> implements MultiaryFunction.TwiceDifferentiable, MultiaryFunction.PureQuadratic {

    public static PureQuadraticFunction makeComplex(final Access2D coefficients) {
        return new PureQuadraticFunction<>(GenericStore.COMPLEX.copy(coefficients));
    }

    public static PureQuadraticFunction makeComplex(final int arity) {
        return new PureQuadraticFunction<>(GenericStore.COMPLEX.make(arity, arity));
    }

    public static PureQuadraticFunction makePrimitive(final Access2D coefficients) {
        return new PureQuadraticFunction<>(Primitive64Store.FACTORY.copy(coefficients));
    }

    public static PureQuadraticFunction makePrimitive(final int arity) {
        return new PureQuadraticFunction<>(Primitive64Store.FACTORY.make(arity, arity));
    }

    public static PureQuadraticFunction makeRational(final Access2D coefficients) {
        return new PureQuadraticFunction<>(GenericStore.RATIONAL.copy(coefficients));
    }

    public static PureQuadraticFunction makeRational(final int arity) {
        return new PureQuadraticFunction<>(GenericStore.RATIONAL.make(arity, arity));
    }

    public static > PureQuadraticFunction wrap(final PhysicalStore coefficients) {
        return new PureQuadraticFunction<>(coefficients);
    }

    private final MatrixStore myCoefficients;
    private final ConstantFunction myConstant;

    PureQuadraticFunction(final MatrixStore coefficients) {

        super();

        if (!coefficients.isSquare()) {
            throw new IllegalArgumentException("Must be sqaure!");
        }

        myCoefficients = coefficients;
        myConstant = new ConstantFunction<>(coefficients.countRows(), coefficients.physical());
    }

    public int arity() {
        return (int) myCoefficients.countColumns();
    }

    public N getConstant() {
        return myConstant.getConstant();
    }

    @Override
    public MatrixStore getGradient(final Access1D point) {

        final PhysicalStore retVal = myCoefficients.physical().make(this.arity(), 1L);

        this.getHessian(point).multiply(point, retVal);

        return retVal;
    }

    @Override
    public MatrixStore getHessian(final Access1D point) {
        return myCoefficients.add(myCoefficients.conjugate());
    }

    public MatrixStore getLinearFactors() {
        return myCoefficients.physical().builder().makeZero(this.arity(), 1L).get();
    }

    @Override
    public N invoke(final Access1D arg) {
        return this.getScalarValue(arg).get();
    }

    public PhysicalStore quadratic() {
        return (PhysicalStore) myCoefficients;
    }

    public void setConstant(final Comparable constant) {
        myConstant.setConstant(constant);
    }

    Factory factory() {
        return myCoefficients.physical();
    }

    Scalar getScalarValue(final Access1D arg) {

        Scalar retVal = myConstant.getScalarConstant();

        retVal = retVal.add(myCoefficients.multiplyBoth(arg));

        return retVal;
    }

}