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A fast and easy to use dense and sparse matrix linear algebra library written in Java.
There is a newer version: 0.43.1
/*
 * Copyright (c) 2009-2020, Peter Abeles. All Rights Reserved.
 *
 * This file is part of Efficient Java Matrix Library (EJML).
 *
 * Licensed 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.ejml.equation;

import org.ejml.data.DMatrixRMaj;
import org.ejml.dense.row.CommonOps_DDRM;

import java.util.ArrayList;
import java.util.List;

/**
 * matrix used to construct a matrix from a sequence of concatenations.
 *
 * @author Peter Abeles
 */
public class MatrixConstructor {

    VariableMatrix output;
    List items = new ArrayList();

    public MatrixConstructor( ManagerTempVariables manager ) {
        this.output = manager.createMatrix();
    }

    public void addToRow( Variable variable ) {
        if (variable.getType() == VariableType.INTEGER_SEQUENCE) {
            if (((VariableIntegerSequence)variable).sequence.requiresMaxIndex())
                throw new ParseError("Trying to create a matrix with an unbounded integer range." +
                        " Forgot a value after a colon?");
        }
        items.add(new Item(variable));
    }

    public void endRow() {
        items.add(new Item());
    }

    public void construct() {
        // make sure the last item is and end row
        if (!items.get(items.size() - 1).endRow)
            endRow();

        // have to initialize some variable types first to get the actual size
        for (int i = 0; i < items.size(); i++) {
            items.get(i).initialize();
        }

        setToRequiredSize(output.matrix);

        int matrixRow = 0;
        List row = new ArrayList();
        for (int i = 0; i < items.size(); i++) {
            Item item = items.get(i);

            if (item.endRow) {
                int expectedRows = 0;
                int numCols = 0;
                for (int j = 0; j < row.size(); j++) {
                    Item v = row.get(j);

                    int numRows = v.getRows();

                    if (j == 0) {
                        expectedRows = numRows;
                    } else if (v.getRows() != expectedRows) {
                        throw new RuntimeException("Row miss-matched. " + numRows + " " + v.getRows());
                    }

                    if (v.matrix) {
                        CommonOps_DDRM.insert(v.getMatrix(), output.matrix, matrixRow, numCols);
                    } else if (v.variable.getType() == VariableType.SCALAR) {
                        output.matrix.set(matrixRow, numCols, v.getValue());
                    } else if (v.variable.getType() == VariableType.INTEGER_SEQUENCE) {
                        IntegerSequence sequence = ((VariableIntegerSequence)v.variable).sequence;
                        int col = numCols;
                        while (sequence.hasNext()) {
                            output.matrix.set(matrixRow, col++, sequence.next());
                        }
                    } else {
                        throw new ParseError("Can't insert a variable of type " + v.variable.getType() + " inside a matrix!");
                    }
                    numCols += v.getColumns();
                }

                matrixRow += expectedRows;
                row.clear();
            } else {
                row.add(item);
            }
        }
    }

    public VariableMatrix getOutput() {
        return output;
    }

    protected void setToRequiredSize( DMatrixRMaj matrix ) {


        int matrixRow = 0;
        int matrixCol = 0;
        List row = new ArrayList();
        for (int i = 0; i < items.size(); i++) {
            Item item = items.get(i);

            if (item.endRow) {
                Item v = row.get(0);
                int numRows = v.getRows();
                int numCols = v.getColumns();
                for (int j = 1; j < row.size(); j++) {
                    v = row.get(j);
                    if (v.getRows() != numRows)
                        throw new RuntimeException("Row miss-matched. " + numRows + " " + v.getRows());
                    numCols += v.getColumns();
                }
                matrixRow += numRows;

                if (matrixCol == 0)
                    matrixCol = numCols;
                else if (matrixCol != numCols)
                    throw new ParseError("Row " + matrixRow + " has an unexpected number of columns; expected = " + matrixCol + " found = " + numCols);

                row.clear();
            } else {
                row.add(item);
            }
        }

        matrix.reshape(matrixRow, matrixCol);
    }

    @SuppressWarnings("NullAway.Init")
    private static class Item {
        Variable variable;
        boolean endRow;
        boolean matrix;

        private Item( Variable variable ) {
            this.variable = variable;
            matrix = variable instanceof VariableMatrix;
        }

        private Item() {
            endRow = true;
        }

        public int getRows() {
            if (matrix) {
                return ((VariableMatrix)variable).matrix.numRows;
            } else {
                return 1;
            }
        }

        public int getColumns() {
            if (matrix) {
                return ((VariableMatrix)variable).matrix.numCols;
            } else if (variable.getType() == VariableType.SCALAR) {
                return 1;
            } else if (variable.getType() == VariableType.INTEGER_SEQUENCE) {
                return ((VariableIntegerSequence)variable).sequence.length();
            } else {
                throw new RuntimeException("BUG! Should have been caught earlier");
            }
        }

        public DMatrixRMaj getMatrix() {
            return ((VariableMatrix)variable).matrix;
        }

        public double getValue() {
            return ((VariableScalar)variable).getDouble();
        }

        public void initialize() {
            if (variable != null && !matrix && variable.getType() == VariableType.INTEGER_SEQUENCE) {
                ((VariableIntegerSequence)variable).sequence.initialize(-1);
            }
        }
    }
}