| // Licensed to the Apache Software Foundation (ASF) under one |
| // or more contributor license agreements. See the NOTICE file |
| // distributed with this work for additional information |
| // regarding copyright ownership. The ASF licenses this file |
| // to you 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.spaceroots.mantissa.linalg; |
| |
| /** This class implements lower triangular matrices of linear algebra. |
| |
| * @version $Id$ |
| * @author L. Maisonobe |
| |
| */ |
| |
| public class LowerTriangularMatrix |
| extends SquareMatrix { |
| |
| /** Simple constructor. |
| * This constructor builds a lower triangular matrix of specified order, all |
| * elements being zeros. |
| * @param order order of the matrix |
| */ |
| public LowerTriangularMatrix(int order) { |
| super(order); |
| } |
| |
| /** Simple constructor. |
| * Build a matrix with specified elements. |
| * @param order order of the matrix |
| * @param data table of the matrix elements (stored row after row) |
| */ |
| public LowerTriangularMatrix(int order, double[] data) { |
| super(order, data); |
| } |
| |
| /** Copy constructor. |
| * @param l lower triangular matrix to copy |
| */ |
| public LowerTriangularMatrix(LowerTriangularMatrix l) { |
| super(l); |
| } |
| |
| public Matrix duplicate() { |
| return new LowerTriangularMatrix(this); |
| } |
| |
| public void setElement(int i, int j, double value) { |
| if (i < j) { |
| throw new ArrayIndexOutOfBoundsException("cannot set elements" |
| + " above diagonal of a" |
| + " lower triangular matrix"); |
| } |
| super.setElement(i, j, value); |
| } |
| |
| /** Add a matrix to the instance. |
| * This method adds a matrix to the instance. It does modify the instance. |
| * @param l lower triangular matrix to add |
| * @exception IllegalArgumentException if there is a dimension mismatch |
| */ |
| public void selfAdd(LowerTriangularMatrix l) { |
| |
| // validity check |
| if ((rows != l.rows) || (columns != l.columns)) { |
| throw new IllegalArgumentException("cannot add a " |
| + l.rows + 'x' + l.columns |
| + " matrix to a " |
| + rows + 'x' + columns |
| + " matrix"); |
| } |
| |
| // addition loop |
| for (int i = 0; i < rows; ++i) { |
| for (int index = i * columns; index < i * (columns + 1) + 1; ++index) { |
| data[index] += l.data[index]; |
| } |
| } |
| |
| } |
| |
| /** Substract a matrix from the instance. |
| * This method substract a matrix from the instance. It does modify the instance. |
| * @param l lower triangular matrix to substract |
| * @exception IllegalArgumentException if there is a dimension mismatch |
| */ |
| public void selfSub(LowerTriangularMatrix l) { |
| |
| // validity check |
| if ((rows != l.rows) || (columns != l.columns)) { |
| throw new IllegalArgumentException("cannot substract a " |
| + l.rows + 'x' + l.columns |
| + " matrix from a " |
| + rows + 'x' + columns |
| + " matrix"); |
| } |
| |
| // substraction loop |
| for (int i = 0; i < rows; ++i) { |
| for (int index = i * columns; index < i * (columns + 1) + 1; ++index) { |
| data[index] -= l.data[index]; |
| } |
| } |
| |
| } |
| |
| public double getDeterminant(double epsilon) { |
| double determinant = data[0]; |
| for (int index = columns + 1; index < columns * columns; index += columns + 1) { |
| determinant *= data[index]; |
| } |
| return determinant; |
| } |
| |
| public Matrix solve(Matrix b, double epsilon) |
| throws SingularMatrixException { |
| // validity check |
| if (b.getRows () != rows) { |
| throw new IllegalArgumentException("dimension mismatch"); |
| } |
| |
| // prepare the data storage |
| int bRows = b.getRows(); |
| int bCols = b.getColumns(); |
| |
| double[] resultData = new double[bRows * bCols]; |
| int resultIndex = 0; |
| int lowerElements = 0; |
| int upperElements = 0; |
| int minJ = columns; |
| int maxJ = 0; |
| |
| // solve the linear system |
| for (int i = 0; i < rows; ++i) { |
| double diag = data[i * (columns + 1)]; |
| if (Math.abs(diag) < epsilon) { |
| throw new SingularMatrixException(); |
| } |
| double inv = 1.0 / diag; |
| |
| NonNullRange range = b.getRangeForRow(i); |
| minJ = Math.min(minJ, range.begin); |
| maxJ = Math.max(maxJ, range.end); |
| |
| int j = 0; |
| while (j < minJ) { |
| resultData[resultIndex] = 0.0; |
| ++resultIndex; |
| ++j; |
| } |
| |
| // compute the possibly non null elements |
| int bIndex = i * bCols + minJ; |
| while (j < maxJ) { |
| |
| // compute the current element |
| int index1 = i * columns; |
| int index2 = j; |
| double value = b.data[bIndex]; |
| while (index1 < i * (columns + 1)) { |
| value -= data[index1] * resultData[index2]; |
| ++index1; |
| index2 += bCols; |
| } |
| value *= inv; |
| resultData[resultIndex] = value; |
| |
| // count the affected upper and lower elements |
| // (in order to deduce the shape of the resulting matrix) |
| if (j < i) { |
| ++lowerElements; |
| } else if (i < j) { |
| ++upperElements; |
| } |
| |
| ++bIndex; |
| ++resultIndex; |
| ++j; |
| |
| } |
| |
| while (j < bCols) { |
| resultData[resultIndex] = 0.0; |
| ++resultIndex; |
| ++j; |
| } |
| |
| } |
| |
| return MatrixFactory.buildMatrix(bRows, bCols, resultData, |
| lowerElements, upperElements); |
| |
| } |
| |
| public NonNullRange getRangeForRow(int i) { |
| return new NonNullRange(0, i + 1); |
| } |
| |
| public NonNullRange getRangeForColumn(int j) { |
| return new NonNullRange(j, rows); |
| } |
| |
| private static final long serialVersionUID = 3592505328858227281L; |
| |
| } |