DiagonalMatrix extends AbstractRealMatrix implements Serializable { @Override public double[] operate(final double[] v) throws DimensionMismatchException { return multiply(new DiagonalMatrix(v, false)).getDataRef(); } DiagonalMatrix(final int dimension);  DiagonalMatrix(final double[] d);  DiagonalMatrix(final double[] d, final boolean copyArray); @Override RealMatrix createMatrix(final int rowDimension,
                                   final int columnDimension); @Override RealMatrix copy(); DiagonalMatrix add(final DiagonalMatrix m); DiagonalMatrix subtract(final DiagonalMatrix m); DiagonalMatrix multiply(final DiagonalMatrix m); @Override RealMatrix multiply(final RealMatrix m); @Override double[][] getData(); double[] getDataRef(); @Override double getEntry(final int row, final int column); @Override void setEntry(final int row, final int column, final double value); @Override void addToEntry(final int row,
                           final int column,
                           final double increment); @Override void multiplyEntry(final int row,
                              final int column,
                              final double factor); @Override int getRowDimension(); @Override int getColumnDimension(); @Override double[] operate(final double[] v); @Override double[] preMultiply(final double[] v); @Override RealVector preMultiply(final RealVector v); DiagonalMatrix inverse(); DiagonalMatrix inverse(double threshold); boolean isSingular(double threshold);  }
@Test public void testOperate() { final double[] data = { -1.2, 3.4, 5 }; final DiagonalMatrix diag = new DiagonalMatrix(data); final RealMatrix dense = new Array2DRowRealMatrix(diag.getData()); final double[] v = { 6.7, 890.1, 23.4 }; final double[] diagResult = diag.operate(v); final double[] denseResult = dense.operate(v); TestUtils.assertEquals(diagResult, denseResult, 0d); }