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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.utils;

import cc.redberry.core.context.CC;
import cc.redberry.core.indices.IndexType;
import cc.redberry.core.indices.SimpleIndices;
import cc.redberry.core.tensor.SimpleTensor;

import static cc.redberry.core.indices.IndicesUtils.getState;

/**
 * Utils fot matrices.
 *
 * @author Dmitry Bolotin
 * @author Stanislav Poslavsky
 * @since 1.1.7
 */
public final class MatrixUtils {
    private MatrixUtils() {
    }

    /**
     * Returns whether specified tensor is matrix of specified type and with specified signature.
     *
     * @param tensor simple tensor
     * @param type   type of matrix
     * @param upper  number of upper matrix indices
     * @param lower  number of lower matrix indices
     * @return true if specified tensor is matrix of specified type and with specified signature and false in other case
     */
    public static boolean isGeneralizedMatrix(SimpleTensor tensor, IndexType type, int upper, int lower) {
        if (CC.isMetric(type))
            throw new IllegalArgumentException("Matrices can not be of metric type.");
        SimpleIndices indices = tensor.getIndices().getOfType(type);
        int i = 0;
        for (; i < upper; ++i)
            if (!getState(indices.get(i)))
                return false;
        upper += lower;
        for (; i < upper; ++i)
            if (getState(indices.get(i)))
                return false;
        return true;
    }

    /**
     * Returns whether specified tensor is matrix of specified type.
     *
     * @param tensor simple tensor
     * @param type   type of matrix
     * @return true if specified tensor is matrix of specified type and false in other case
     */
    public static boolean isMatrix(SimpleTensor tensor, IndexType type) {
        return isGeneralizedMatrix(tensor, type, 1, 1);
    }

    /**
     * Returns whether specified tensor is vector of specified type.
     *
     * @param tensor simple tensor
     * @param type   type of matrix
     * @return true if specified tensor is vector of specified type and false in other case
     */
    public static boolean isVector(SimpleTensor tensor, IndexType type) {
        return isGeneralizedMatrix(tensor, type, 1, 0);
    }

    /**
     * Returns whether specified tensor is covector of specified type.
     *
     * @param tensor simple tensor
     * @param type   type of matrix
     * @return true if specified tensor is covector of specified type and false in other case
     */
    public static boolean isCovector(SimpleTensor tensor, IndexType type) {
        return isGeneralizedMatrix(tensor, type, 0, 1);
    }
}