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Redberry is an open source computer algebra system designed for tensor manipulation. It implements basic computer algebra system routines as well as complex tools for real computations in physics. This is Redberry core, which contains the implementation of the basic computer algebra routines and general-purpose transformations.

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/*
 * Redberry: symbolic tensor computations.
 *
 * Copyright (c) 2010-2013:
 *   Stanislav Poslavsky   
 *   Bolotin Dmitriy       
 *
 * This file is part of Redberry.
 *
 * Redberry is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Redberry is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Redberry. If not, see .
 */
package cc.redberry.core.indices;

import cc.redberry.core.indexmapping.IndexMapping;

/**
 * This class is an implementation of {@link Indices} interface and represents
 * empty indices, i.e. indices that do not contains any index. For
 * example, if we have tensor X, method {@link cc.redberry.core.tensor.Tensor#getIndices()
 * } will return {@code EmptySimpleIndices}, that means that X is scalar. This
 * class is singleton, and you can get instance throughout { @code EMPTY_SIMPLE_INDICES_INSTANCE}
 * field.
 *
 * @author Dmitry Bolotin
 * @author Stanislav Poslavsky
 * @since 1.0
 */
final class EmptySimpleIndices extends EmptyIndices implements SimpleIndices {

    /**
     * Instance of {@code EmptySimpleIndices}
     */
    static final EmptySimpleIndices EMPTY_SIMPLE_INDICES_INSTANCE = new EmptySimpleIndices();

    EmptySimpleIndices() {
    }

    /**
     * Returns {@code EmptySimpleIndices} instance
     *
     * @return {@code EmptySimpleIndices} instance
     */
    @Override
    public SimpleIndices getInverted() {
        return this;
    }

    /**
     * Returns {@code EmptySimpleIndices} instance
     *
     * @return {@code EmptySimpleIndices} instance
     */
    @Override
    public SimpleIndices getFree() {
        return this;
    }

    /**
     * Returns {@code EmptySimpleIndices} instance
     *
     * @return {@code EmptySimpleIndices} instance
     */
    @Override
    public SimpleIndices getOfType(IndexType type) {
        return this;
    }

    /**
     * Doing nothing
     */
    @Override
    public void setSymmetries(IndicesSymmetries symmetries) {
        if (symmetries.getStructureOfIndices().size() != 0)
            throw new IllegalArgumentException("Symmetries dimensions are not equal to indices size.");
    }

    /**
     * Returns {@code Symmetries.EMPTY_SYMMETRIES}
     *
     * @return {@code Symmetries.EMPTY_SYMMETRIES}
     */
    @Override
    public IndicesSymmetries getSymmetries() {
        return IndicesSymmetries.EMPTY_SYMMETRIES;
    }

    /**
     * Do nothing.
     *
     * @param mapping
     * @return false
     */
    @Override
    public SimpleIndices applyIndexMapping(IndexMapping mapping) {
        return this;
    }

    /**
     * {@inheritDoc}
     *
     * @param obj {@inheritDoc}
     * @return {@inheritDoc}
     */
    @Override
    public boolean equals(Object obj) {
        return obj == this; // :))
    }

    /**
     * Returns {@code equals(indices)}
     *
     * @param indices indices to compare
     * @return {@code equals(indices)}
     */
    @Override
    public boolean equalsWithSymmetries(SimpleIndices indices) {
        return indices == EMPTY_SIMPLE_INDICES_INSTANCE; //There is only one instance of empty SimpleIndices
    }

    /**
     * Returns 1
     *
     * @return 1
     */
    @Override
    public int hashCode() {
        return 453679;
    }

    @Override
    public StructureOfIndices getStructureOfIndices() {
        return StructureOfIndices.EMPTY;
    }
}