/*
    * 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
    *
    *      https://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.
   */
  
  /*
   * This is not the original file distributed by the Apache Software Foundation
   * It has been modified by the Hipparchus project
   */
  package org.hipparchus.linear;
  
  import java.io.Serializable;
  
  import org.hipparchus.exception.LocalizedCoreFormats;
  import org.hipparchus.exception.MathIllegalArgumentException;
  import org.hipparchus.exception.NullArgumentException;
  import org.hipparchus.util.FastMath;
  import org.hipparchus.util.MathUtils;
  import org.hipparchus.util.Precision;
  
  /**
   * Implementation of a diagonal matrix.
   *
   */
  public class DiagonalMatrix extends AbstractRealMatrix
      implements Serializable {
      /** Serializable version identifier. */
      private static final long serialVersionUID = 20121229L;
      /** Entries of the diagonal. */
      private final double[] data;
  
      /**
       * Creates a matrix with the supplied dimension.
       *
       * @param dimension Number of rows and columns in the new matrix.
       * @throws MathIllegalArgumentException if the dimension is
       * not positive.
       */
      public DiagonalMatrix(final int dimension)
          throws MathIllegalArgumentException {
          super(dimension, dimension);
          data = new double[dimension];
      }
  
      /**
       * Creates a matrix using the input array as the underlying data.
       * <br>
       * The input array is copied, not referenced.
       *
       * @param d Data for the new matrix.
       */
      public DiagonalMatrix(final double[] d) {
          this(d, true);
      }
  
      /**
       * Creates a matrix using the input array as the underlying data.
       * <br>
       * If an array is created specially in order to be embedded in a
       * this instance and not used directly, the {@code copyArray} may be
       * set to {@code false}.
       * This will prevent the copying and improve performance as no new
       * array will be built and no data will be copied.
       *
       * @param d Data for new matrix.
       * @param copyArray if {@code true}, the input array will be copied,
       * otherwise it will be referenced.
       * @exception NullArgumentException if d is null
       */
      public DiagonalMatrix(final double[] d, final boolean copyArray)
          throws NullArgumentException {
          MathUtils.checkNotNull(d);
          data = copyArray ? d.clone() : d;
      }
  
      /**
       * {@inheritDoc}
       *
       * @throws MathIllegalArgumentException if the requested dimensions are not equal.
       */
      @Override
      public RealMatrix createMatrix(final int rowDimension,
                                     final int columnDimension)
          throws MathIllegalArgumentException {
          if (rowDimension != columnDimension) {
              throw new MathIllegalArgumentException(LocalizedCoreFormats.DIMENSIONS_MISMATCH,
                                                     rowDimension, columnDimension);
         }
 
         return new DiagonalMatrix(rowDimension);
     }
 
     /** {@inheritDoc} */
     @Override
     public RealMatrix copy() {
         return new DiagonalMatrix(data);
     }
 
     /**
      * Compute the sum of {@code this} and {@code m}.
      *
      * @param m Matrix to be added.
      * @return {@code this + m}.
      * @throws MathIllegalArgumentException if {@code m} is not the same
      * size as {@code this}.
      */
     public DiagonalMatrix add(final DiagonalMatrix m)
         throws MathIllegalArgumentException {
         // Safety check.
         MatrixUtils.checkAdditionCompatible(this, m);
 
         final int dim = getRowDimension();
         final double[] outData = new double[dim];
         for (int i = 0; i < dim; i++) {
             outData[i] = data[i] + m.data[i];
         }
 
         return new DiagonalMatrix(outData, false);
     }
 
     /**
      * Returns {@code this} minus {@code m}.
      *
      * @param m Matrix to be subtracted.
      * @return {@code this - m}
      * @throws MathIllegalArgumentException if {@code m} is not the same
      * size as {@code this}.
      */
     public DiagonalMatrix subtract(final DiagonalMatrix m)
         throws MathIllegalArgumentException {
         MatrixUtils.checkSubtractionCompatible(this, m);
 
         final int dim = getRowDimension();
         final double[] outData = new double[dim];
         for (int i = 0; i < dim; i++) {
             outData[i] = data[i] - m.data[i];
         }
 
         return new DiagonalMatrix(outData, false);
     }
 
     /**
      * Returns the result of postmultiplying {@code this} by {@code m}.
      *
      * @param m matrix to postmultiply by
      * @return {@code this * m}
      * @throws MathIllegalArgumentException if
      * {@code columnDimension(this) != rowDimension(m)}
      */
     public DiagonalMatrix multiply(final DiagonalMatrix m)
         throws MathIllegalArgumentException {
         MatrixUtils.checkMultiplicationCompatible(this, m);
 
         final int dim = getRowDimension();
         final double[] outData = new double[dim];
         for (int i = 0; i < dim; i++) {
             outData[i] = data[i] * m.data[i];
         }
 
         return new DiagonalMatrix(outData, false);
     }
 
     /** {@inheritDoc} */
     @Override
     public RealMatrix multiply(final RealMatrix m)
         throws MathIllegalArgumentException {
         if (m instanceof DiagonalMatrix) {
             return multiply((DiagonalMatrix) m);
         } else {
             MatrixUtils.checkMultiplicationCompatible(this, m);
             final RealMatrix product = m.createMatrix(m.getRowDimension(), m.getColumnDimension());
             product.walkInOptimizedOrder(new DefaultRealMatrixChangingVisitor() {
                 /** {@inheritDoc} */
                 @Override
                 public double visit(int row, int column, double value) {
                     return data[row] * m.getEntry(row, column);
                 }
             });
             return product;
         }
     }
 
     /**
      * Returns the result of postmultiplying {@code this} by {@code m^T}.
      * @param m matrix to first transpose and second postmultiply by
      * @return {@code this * m}
      * @throws MathIllegalArgumentException if
      * {@code columnDimension(this) != columnDimension(m)}
      * @since 1.3
      */
     public DiagonalMatrix multiplyTransposed(final DiagonalMatrix m)
         throws MathIllegalArgumentException {
         // transposition is no-op for diagonal matrices
         return multiply(m);
     }
 
     /** {@inheritDoc} */
     @Override
     public RealMatrix multiplyTransposed(final RealMatrix m)
         throws MathIllegalArgumentException {
         if (m instanceof DiagonalMatrix) {
             return multiplyTransposed((DiagonalMatrix) m);
         } else {
             MatrixUtils.checkSameColumnDimension(this, m);
             final RealMatrix product = m.createMatrix(m.getColumnDimension(), m.getRowDimension());
             product.walkInOptimizedOrder(new DefaultRealMatrixChangingVisitor() {
                 /** {@inheritDoc} */
                 @Override
                 public double visit(int row, int column, double value) {
                     return data[row] * m.getEntry(column, row);
                 }
             });
             return product;
         }
     }
 
     /**
      * Returns the result of postmultiplying {@code this^T} by {@code m}.
      * @param m matrix to first transpose and second postmultiply by
      * @return {@code this^T * m}
      * @throws MathIllegalArgumentException if
      * {@code columnDimension(this) != columnDimension(m)}
      * @since 1.3
      */
     public DiagonalMatrix transposeMultiply(final DiagonalMatrix m)
         throws MathIllegalArgumentException {
         // transposition is no-op for diagonal matrices
         return multiply(m);
     }
 
     /** {@inheritDoc} */
     @Override
     public RealMatrix transposeMultiply(final RealMatrix m) {
         if (m instanceof DiagonalMatrix) {
             return transposeMultiply((DiagonalMatrix) m);
         } else {
             // transposition is no-op for diagonal matrices
             return multiply(m);
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public double[][] getData() {
         final int dim = getRowDimension();
         final double[][] out = new double[dim][dim];
 
         for (int i = 0; i < dim; i++) {
             out[i][i] = data[i];
         }
 
         return out;
     }
 
     /**
      * Gets a reference to the underlying data array.
      *
      * @return 1-dimensional array of entries.
      */
     public double[] getDataRef() {
         return data; // NOPMD - returning an internal array is intentional and documented here
     }
 
     /** {@inheritDoc} */
     @Override
     public double getEntry(final int row, final int column)
         throws MathIllegalArgumentException {
         MatrixUtils.checkMatrixIndex(this, row, column);
         return row == column ? data[row] : 0;
     }
 
     /** {@inheritDoc}
      * @throws MathIllegalArgumentException if {@code row != column} and value is non-zero.
      */
     @Override
     public void setEntry(final int row, final int column, final double value)
         throws MathIllegalArgumentException {
         if (row == column) {
             MatrixUtils.checkRowIndex(this, row);
             data[row] = value;
         } else {
             ensureZero(value);
         }
     }
 
     /** {@inheritDoc}
      * @throws MathIllegalArgumentException if {@code row != column} and increment is non-zero.
      */
     @Override
     public void addToEntry(final int row,
                            final int column,
                            final double increment)
         throws MathIllegalArgumentException {
         if (row == column) {
             MatrixUtils.checkRowIndex(this, row);
             data[row] += increment;
         } else {
             ensureZero(increment);
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public void multiplyEntry(final int row,
                               final int column,
                               final double factor)
         throws MathIllegalArgumentException {
         // we don't care about non-diagonal elements for multiplication
         if (row == column) {
             MatrixUtils.checkRowIndex(this, row);
             data[row] *= factor;
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public int getRowDimension() {
         return data.length;
     }
 
     /** {@inheritDoc} */
     @Override
     public int getColumnDimension() {
         return data.length;
     }
 
     /** {@inheritDoc} */
     @Override
     public double[] operate(final double[] v)
         throws MathIllegalArgumentException {
         return multiply(new DiagonalMatrix(v, false)).getDataRef();
     }
 
     /** {@inheritDoc} */
     @Override
     public double[] preMultiply(final double[] v)
         throws MathIllegalArgumentException {
         return operate(v);
     }
 
     /** {@inheritDoc} */
     @Override
     public RealVector preMultiply(final RealVector v) throws MathIllegalArgumentException {
         final double[] vectorData;
         if (v instanceof ArrayRealVector) {
             vectorData = ((ArrayRealVector) v).getDataRef();
         } else {
             vectorData = v.toArray();
         }
         return MatrixUtils.createRealVector(preMultiply(vectorData));
     }
 
     /** Ensure a value is zero.
      * @param value value to check
      * @exception MathIllegalArgumentException if value is not zero
      */
     private void ensureZero(final double value) throws MathIllegalArgumentException {
         if (!Precision.equals(0.0, value, 1)) {
             throw new MathIllegalArgumentException(LocalizedCoreFormats.NUMBER_TOO_LARGE,
                                                    FastMath.abs(value), 0);
         }
     }
 
     /**
      * Computes the inverse of this diagonal matrix.
      * <p>
      * Note: this method will use a singularity threshold of 0,
      * use {@link #inverse(double)} if a different threshold is needed.
      *
      * @return the inverse of {@code m}
      * @throws MathIllegalArgumentException if the matrix is singular
      */
     public DiagonalMatrix inverse() throws MathIllegalArgumentException {
         return inverse(0);
     }
 
     /**
      * Computes the inverse of this diagonal matrix.
      *
      * @param threshold Singularity threshold.
      * @return the inverse of {@code m}
      * @throws MathIllegalArgumentException if the matrix is singular
      */
     public DiagonalMatrix inverse(double threshold) throws MathIllegalArgumentException {
         if (isSingular(threshold)) {
             throw new MathIllegalArgumentException(LocalizedCoreFormats.SINGULAR_MATRIX);
         }
 
         final double[] result = new double[data.length];
         for (int i = 0; i < data.length; i++) {
             result[i] = 1.0 / data[i];
         }
         return new DiagonalMatrix(result, false);
     }
 
     /** Returns whether this diagonal matrix is singular, i.e. any diagonal entry
      * is equal to {@code 0} within the given threshold.
      *
      * @param threshold Singularity threshold.
      * @return {@code true} if the matrix is singular, {@code false} otherwise
      */
     public boolean isSingular(double threshold) {
         for (int i = 0; i < data.length; i++) {
             if (Precision.equals(data[i], 0.0, threshold)) {
                 return true;
             }
         }
         return false;
     }
 }