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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) 2010-2015:
 *   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.indexmapping;

import cc.redberry.core.number.Complex;
import cc.redberry.core.number.NumberUtils;
import cc.redberry.core.tensor.Tensor;

/**
 * {@link cc.redberry.core.tensor.Power}-specific mapping provider.
 *
 * @author Dmitry Bolotin
 * @author Stanislav Poslavsky
 * @since 1.0
 */
class ProviderPower implements IndexMappingProviderFactory {

    static final ProviderPower INSTANCE = new ProviderPower();

    private ProviderPower() {
    }

    @Override
    public IndexMappingProvider create(IndexMappingProvider opu, Tensor from, Tensor to) {
        IndexMappingBuffer exponentMapping = IndexMappings.getFirstBuffer(from.get(1), to.get(1));   //todo try get first positive mapping
        if (exponentMapping == null || exponentMapping.getSign())
            return IndexMappingProvider.Util.EMPTY_PROVIDER;

        //todo two signs are possible
        IndexMappingBuffer baseMapping = IndexMappings.getFirstBuffer(from.get(0), to.get(0));
        if (baseMapping == null)
            return IndexMappingProvider.Util.EMPTY_PROVIDER;

        if (baseMapping.getSign() == false)
            return new DummyIndexMappingProvider(opu);
        if (!(from.get(1) instanceof Complex))
            return IndexMappingProvider.Util.EMPTY_PROVIDER;

        assert to.get(1) instanceof Complex;
        Complex exponent = (Complex) from.get(1);
        if (NumberUtils.isIntegerEven(exponent))
            return new DummyIndexMappingProvider(opu);
        if (NumberUtils.isIntegerOdd(exponent))
            return new MinusIndexMappingProvider(opu);

        return IndexMappingProvider.Util.EMPTY_PROVIDER;
    }
}