示例#1
0
        public void SolveLongMatrixThrowsArgumentException()
        {
            var matrix = new SparseMatrix(3, 2);
            var input = new DenseVector(3);

            var solver = new TFQMR();
            Assert.Throws<ArgumentException>(() => matrix.SolveIterative(input, solver));
        }
示例#2
0
        public void SolveLongMatrixThrowsArgumentException()
        {
            var matrix = new SparseMatrix(3, 2);
            var input = new DenseVector(3);

            var solver = new BiCgStab();
            Assert.That(() => matrix.SolveIterative(input, solver), Throws.ArgumentException);
        }
示例#3
0
        public void SolveWideMatrixThrowsArgumentException()
        {
            var matrix = new SparseMatrix(2, 3);
            var input = new DenseVector(2);

            var solver = new TFQMR();
            Assert.That(() => matrix.SolveIterative(input, solver), Throws.ArgumentException);
        }
示例#4
0
        public void SolveWideMatrixThrowsArgumentException()
        {
            var matrix = new SparseMatrix(2, 3);
            var input = new DenseVector(2);

            var solver = new GpBiCg();
            Assert.Throws<ArgumentException>(() => matrix.SolveIterative(input, solver));
        }
        /// <summary>
        /// Check the result.
        /// </summary>
        /// <param name="preconditioner">Specific preconditioner.</param>
        /// <param name="matrix">Source matrix.</param>
        /// <param name="vector">Initial vector.</param>
        /// <param name="result">Result vector.</param>
        protected override void CheckResult(IPreconditioner<Complex> preconditioner, SparseMatrix matrix, Vector<Complex> vector, Vector<Complex> result)
        {
            Assert.AreEqual(typeof(UnitPreconditioner<Complex>), preconditioner.GetType(), "#01");

            // Unit preconditioner is doing nothing. Vector and result should be equal
            for (var i = 0; i < vector.Count; i++)
            {
                Assert.IsTrue(vector[i] == result[i], "#02-" + i);
            }
        }
        /// <summary>
        /// Create unit matrix.
        /// </summary>
        /// <param name="size">Matrix size.</param>
        /// <returns>New unit matrix.</returns>
        internal SparseMatrix CreateUnitMatrix(int size)
        {
            var matrix = new SparseMatrix(size);
            for (var i = 0; i < size; i++)
            {
                matrix[i, i] = 2;
            }

            return matrix;
        }
        /// <summary>
        /// Check the result.
        /// </summary>
        /// <param name="preconditioner">Specific preconditioner.</param>
        /// <param name="matrix">Source matrix.</param>
        /// <param name="vector">Initial vector.</param>
        /// <param name="result">Result vector.</param>
        protected override void CheckResult(IPreconditioner<Complex> preconditioner, SparseMatrix matrix, Vector<Complex> vector, Vector<Complex> result)
        {
            Assert.AreEqual(typeof(Diagonal), preconditioner.GetType(), "#01");

            // Compute M * result = product
            // compare vector and product. Should be equal
            var product = new DenseVector(result.Count);
            matrix.Multiply(result, product);

            for (var i = 0; i < product.Count; i++)
            {
                Assert.IsTrue(vector[i].Real.AlmostEqual(product[i].Real, -Epsilon.Magnitude()), "#02-" + i);
                Assert.IsTrue(vector[i].Imaginary.AlmostEqual(product[i].Imaginary, -Epsilon.Magnitude()), "#03-" + i);
            }
        }
        public void CanAddSparseMatricesBothWays()
        {
            var m1 = new SparseMatrix(1, 3);
            var m2 = SparseMatrix.OfArray(new Complex[,] {{0, 1, 1}});
            var sum1 = m1 + m2;
            var sum2 = m2 + m1;
            Assert.IsTrue(sum1.Equals(m2));
            Assert.IsTrue(sum1.Equals(sum2));

            var sparseResult = new SparseMatrix(1, 3);
            sparseResult.Add(m2, sparseResult);
            Assert.IsTrue(sparseResult.Equals(sum1));

            sparseResult = SparseMatrix.OfArray(new Complex[,] {{0, 1, 1}});
            sparseResult.Add(m1, sparseResult);
            Assert.IsTrue(sparseResult.Equals(sum1));

            sparseResult = SparseMatrix.OfArray(new Complex[,] {{0, 1, 1}});
            m1.Add(sparseResult, sparseResult);
            Assert.IsTrue(sparseResult.Equals(sum1));

            sparseResult = SparseMatrix.OfArray(new Complex[,] {{0, 1, 1}});
            sparseResult.Add(sparseResult, sparseResult);
            Assert.IsTrue(sparseResult.Equals(2*sum1));

            var denseResult = new DenseMatrix(1, 3);
            denseResult.Add(m2, denseResult);
            Assert.IsTrue(denseResult.Equals(sum1));

            denseResult = DenseMatrix.OfArray(new Complex[,] {{0, 1, 1}});
            denseResult.Add(m1, denseResult);
            Assert.IsTrue(denseResult.Equals(sum1));

            var m3 = DenseMatrix.OfArray(new Complex[,] {{0, 1, 1}});
            var sum3 = m1 + m3;
            var sum4 = m3 + m1;
            Assert.IsTrue(sum3.Equals(m3));
            Assert.IsTrue(sum3.Equals(sum4));
        }
示例#9
0
        /// <summary>
        /// Create a matrix based on this vector in row form (one single row).
        /// </summary>
        /// <returns>This vector as a row matrix.</returns>
        public override Matrix<Complex> ToRowMatrix()
        {
            var matrix = new SparseMatrix(1, Count);
            for (var i = 0; i < NonZerosCount; i++)
            {
                matrix.At(0, _nonZeroIndices[i], _nonZeroValues[i]);
            }

            return matrix;
        }
示例#10
0
        /// <summary>
        /// Create a matrix based on this vector in column form (one single column).
        /// </summary>
        /// <returns>This vector as a column matrix.</returns>
        public override Matrix<Complex> ToColumnMatrix()
        {
            var matrix = new SparseMatrix(Count, 1);
            for (var i = 0; i < NonZerosCount; i++)
            {
                matrix.At(_nonZeroIndices[i], 0, _nonZeroValues[i]);
            }

            return matrix;
        }
示例#11
0
 /// <summary>
 /// Create a new sparse matrix with the diagonal as a copy of the given array.
 /// This new matrix will be independent from the array.
 /// A new memory block will be allocated for storing the matrix.
 /// </summary>
 public static SparseMatrix OfDiagonalArray(int rows, int columns, Complex[] diagonal)
 {
     var m = new SparseMatrix(rows, columns);
     m.SetDiagonal(diagonal);
     return m;
 }
示例#12
0
 /// <summary>
 /// Create a new sparse matrix with the diagonal as a copy of the given vector.
 /// This new matrix will be independent from the vector.
 /// A new memory block will be allocated for storing the matrix.
 /// </summary>
 public static SparseMatrix OfDiagonalVector(int rows, int columns, Vector<Complex> diagonal)
 {
     var m = new SparseMatrix(rows, columns);
     m.SetDiagonal(diagonal);
     return m;
 }
        /// <summary>
        /// Can multiply a matrix with matrix.
        /// </summary>
        /// <param name="nameA">Matrix A name.</param>
        /// <param name="nameB">Matrix B name.</param>
        public override void CanMultiplyMatrixWithMatrixIntoResult(string nameA, string nameB)
        {
            var matrixA = TestMatrices[nameA];
            var matrixB = TestMatrices[nameB];
            var matrixC = new SparseMatrix(matrixA.RowCount, matrixB.ColumnCount);
            matrixA.Multiply(matrixB, matrixC);

            Assert.AreEqual(matrixC.RowCount, matrixA.RowCount);
            Assert.AreEqual(matrixC.ColumnCount, matrixB.ColumnCount);

            for (var i = 0; i < matrixC.RowCount; i++)
            {
                for (var j = 0; j < matrixC.ColumnCount; j++)
                {
                    AssertHelpers.AlmostEqualRelative(matrixA.Row(i)*matrixB.Column(j), matrixC[i, j], 15);
                }
            }
        }
示例#14
0
        public void CanSubtractSparseMatricesBothWays()
        {
            var m1 = new SparseMatrix(1, 3);
            var m2 = SparseMatrix.OfArray(new Complex[,] {{0, 1, 1}});
            var diff1 = m1 - m2;
            var diff2 = m2 - m1;
            Assert.IsTrue(diff1.Equals(m2.Negate()));
            Assert.IsTrue(diff1.Equals(diff2.Negate()));

            var sparseResult = new SparseMatrix(1, 3);
            sparseResult.Subtract(m2, sparseResult);
            Assert.IsTrue(sparseResult.Equals(diff1));

            sparseResult = SparseMatrix.OfArray(new Complex[,] {{0, 1, 1}});
            sparseResult.Subtract(m1, sparseResult);
            Assert.IsTrue(sparseResult.Equals(diff2));

            sparseResult = SparseMatrix.OfArray(new Complex[,] {{0, 1, 1}});
            m1.Subtract(sparseResult, sparseResult);
            Assert.IsTrue(sparseResult.Equals(diff1));

            sparseResult = SparseMatrix.OfArray(new Complex[,] {{0, 1, 1}});
            sparseResult.Subtract(sparseResult, sparseResult);
            Assert.IsTrue(sparseResult.Equals(0*diff1));

            var denseResult = new DenseMatrix(1, 3);
            denseResult.Subtract(m2, denseResult);
            Assert.IsTrue(denseResult.Equals(diff1));

            denseResult = DenseMatrix.OfArray(new Complex[,] {{0, 1, 1}});
            denseResult.Subtract(m1, denseResult);
            Assert.IsTrue(denseResult.Equals(diff2));

            var m3 = DenseMatrix.OfArray(new Complex[,] {{0, 1, 1}});
            var diff3 = m1 - m3;
            var diff4 = m3 - m1;
            Assert.IsTrue(diff3.Equals(m3.Negate()));
            Assert.IsTrue(diff3.Equals(diff4.Negate()));
        }
示例#15
0
 public void CanCreateLargeMatrix()
 {
     const int Order = 1000000;
     var matrix = new SparseMatrix(Order);
     Assert.AreEqual(Order, matrix.RowCount);
     Assert.AreEqual(Order, matrix.ColumnCount);
     Assert.DoesNotThrow(() => matrix[0, 0] = 1);
 }
示例#16
0
        public void CanCreateLargeSparseMatrix()
        {
            var matrix = new SparseMatrix(500, 1000);
            var nonzero = 0;
            var rnd = new System.Random(0);

            for (var i = 0; i < matrix.RowCount; i++)
            {
                for (var j = 0; j < matrix.ColumnCount; j++)
                {
                    var value = rnd.Next(10)*rnd.Next(10)*rnd.Next(10)*rnd.Next(10)*rnd.Next(10);
                    if (value != 0)
                    {
                        nonzero++;
                    }

                    matrix[i, j] = value;
                }
            }

            Assert.AreEqual(matrix.NonZerosCount, nonzero);
        }
        /// <summary>
        /// Create a matrix based on this vector in row form (one single row).
        /// </summary>
        /// <returns>This vector as a row matrix.</returns>
        public override Matrix<Complex> ToRowMatrix()
        {
            var matrix = new SparseMatrix(1, Count);
            for (var i = 0; i < _storage.ValueCount; i++)
            {
                matrix.At(0, _storage.Indices[i], _storage.Values[i]);
            }

            return matrix;
        }
        /// <summary>
        /// Create a matrix based on this vector in column form (one single column).
        /// </summary>
        /// <returns>This vector as a column matrix.</returns>
        public override Matrix<Complex> ToColumnMatrix()
        {
            var matrix = new SparseMatrix(Count, 1);
            for (var i = 0; i < _storage.ValueCount; i++)
            {
                matrix.At(_storage.Indices[i], 0, _storage.Values[i]);
            }

            return matrix;
        }
示例#19
0
        /// <summary>
        /// Outer product of two vectors
        /// </summary>
        /// <param name="u">First vector</param>
        /// <param name="v">Second vector</param>
        /// <returns>Matrix M[i,j] = u[i]*v[j] </returns>
        /// <exception cref="ArgumentNullException">If the u vector is <see langword="null" />.</exception> 
        /// <exception cref="ArgumentNullException">If the v vector is <see langword="null" />.</exception> 
        public static Matrix<Complex> OuterProduct(SparseVector u, SparseVector v)
        {
            if (u == null)
            {
                throw new ArgumentNullException("u");
            }

            if (v == null)
            {
                throw new ArgumentNullException("v");
            }

            var matrix = new SparseMatrix(u.Count, v.Count);
            for (var i = 0; i < u.NonZerosCount; i++)
            {
                for (var j = 0; j < v.NonZerosCount; j++)
                {
                    if (u._nonZeroIndices[i] == v._nonZeroIndices[j])
                    {
                        matrix.At(i, j, u._nonZeroValues[i] * v._nonZeroValues[j]);
                    }
                }
            }

            return matrix;
        }
示例#20
0
        /// <summary>
        /// Returns the transpose of this matrix.
        /// </summary>        
        /// <returns>The transpose of this matrix.</returns>
        public override Matrix<Complex> Transpose()
        {
            var ret = new SparseMatrix(ColumnCount, RowCount)
            {
                _columnIndices = new int[NonZerosCount],
                _nonZeroValues = new Complex[NonZerosCount]
            };

            // Do an 'inverse' CopyTo iterate over the rows
            for (var i = 0; i < _rowIndex.Length; i++)
            {
                // Get the begin / end index for the current row
                var startIndex = _rowIndex[i];
                var endIndex = i < _rowIndex.Length - 1 ? _rowIndex[i + 1] : NonZerosCount;

                // Get the values for the current row
                if (startIndex == endIndex)
                {
                    // Begin and end are equal. There are no values in the row, Move to the next row
                    continue;
                }

                for (var j = startIndex; j < endIndex; j++)
                {
                    ret.SetValueAt(_columnIndices[j], i, _nonZeroValues[j]);
                }
            }

            return ret;
        }
示例#21
0
        public void SolvePoissonMatrixAndBackMultiply()
        {
            // Create the matrix
            var matrix = new SparseMatrix(100);

            // Assemble the matrix. We assume we're solving the Poisson equation
            // on a rectangular 10 x 10 grid
            const int GridSize = 10;

            // The pattern is:
            // 0 .... 0 -1 0 0 0 0 0 0 0 0 -1 4 -1 0 0 0 0 0 0 0 0 -1 0 0 ... 0
            for (var i = 0; i < matrix.RowCount; i++)
            {
                // Insert the first set of -1's
                if (i > (GridSize - 1))
                {
                    matrix[i, i - GridSize] = -1;
                }

                // Insert the second set of -1's
                if (i > 0)
                {
                    matrix[i, i - 1] = -1;
                }

                // Insert the centerline values
                matrix[i, i] = 4;

                // Insert the first trailing set of -1's
                if (i < matrix.RowCount - 1)
                {
                    matrix[i, i + 1] = -1;
                }

                // Insert the second trailing set of -1's
                if (i < matrix.RowCount - GridSize)
                {
                    matrix[i, i + GridSize] = -1;
                }
            }

            // Create the y vector
            var y = Vector<Complex>.Build.Dense(matrix.RowCount, 1);

            // Create an iteration monitor which will keep track of iterative convergence
            var monitor = new Iterator<Complex>(
                new IterationCountStopCriterium<Complex>(MaximumIterations),
                new ResidualStopCriterium<Complex>(ConvergenceBoundary),
                new DivergenceStopCriterium<Complex>(),
                new FailureStopCriterium<Complex>());

            var solver = new TFQMR();

            // Solve equation Ax = y
            var x = matrix.SolveIterative(y, solver, monitor);

            // Now compare the results
            Assert.IsNotNull(x, "#02");
            Assert.AreEqual(y.Count, x.Count, "#03");

            // Back multiply the vector
            var z = matrix.Multiply(x);

            // Check that the solution converged
            Assert.IsTrue(monitor.Status == IterationStatus.Converged, "#04");

            // Now compare the vectors
            Assert.LessOrEqual(Distance.Chebyshev(y, z), 2*ConvergenceBoundary);
        }
        /// <summary>
        /// Creates a new  <see cref="SparseMatrix"/> and inserts the given column at the given index.
        /// </summary>
        /// <param name="columnIndex">The index of where to insert the column.</param>
        /// <param name="column">The column to insert.</param>
        /// <returns>A new <see cref="SparseMatrix"/> with the inserted column.</returns>
        /// <exception cref="ArgumentOutOfRangeException">If <paramref name="columnIndex"/> is &lt; zero or &gt; the number of columns.</exception>
        /// <exception cref="ArgumentException">If the size of <paramref name="column"/> != the number of rows.</exception>
        public override Matrix<Complex> InsertColumn(int columnIndex, Vector<Complex> column)
        {
            if (columnIndex < 0 || columnIndex > ColumnCount)
            {
                throw new ArgumentOutOfRangeException("columnIndex");
            }

            if (column.Count != RowCount)
            {
                throw new ArgumentException(Resources.ArgumentMatrixSameRowDimension, "column");
            }

            var result = new SparseMatrix(RowCount, ColumnCount + 1);

            for (var i = 0; i < columnIndex; i++)
            {
                result.SetColumn(i, Column(i));
            }

            result.SetColumn(columnIndex, column);

            for (var i = columnIndex + 1; i < ColumnCount + 1; i++)
            {
                result.SetColumn(i, Column(i - 1));
            }

            return result;
        }
示例#23
0
        /// <summary>
        /// Stacks this matrix on top of the given matrix and places the result into the result <see cref="SparseMatrix"/>.
        /// </summary>
        /// <param name="lower">The matrix to stack this matrix upon.</param>
        /// <returns>The combined <see cref="SparseMatrix"/>.</returns>
        /// <exception cref="ArgumentNullException">If lower is <see langword="null" />.</exception>
        /// <exception cref="ArgumentException">If <strong>upper.Columns != lower.Columns</strong>.</exception>
        public override Matrix<Complex> Stack(Matrix<Complex> lower)
        {
            if (lower == null)
            {
                throw new ArgumentNullException("lower");
            }

            if (lower.ColumnCount != ColumnCount)
            {
                throw new ArgumentException(Resources.ArgumentMatrixSameColumnDimension, "lower");
            }

            var result = new SparseMatrix(RowCount + lower.RowCount, ColumnCount);
            Stack(lower, result);
            return result;
        }
示例#24
0
 /// <summary>
 /// Create a new sparse matrix with the diagonal as a copy of the given vector.
 /// This new matrix will be independent from the vector.
 /// A new memory block will be allocated for storing the matrix.
 /// </summary>
 public static SparseMatrix OfDiagonalVector(Vector<Complex> diagonal)
 {
     var m = new SparseMatrix(diagonal.Count, diagonal.Count);
     m.SetDiagonal(diagonal);
     return m;
 }
 /// <summary>
 /// Check the result.
 /// </summary>
 /// <param name="preconditioner">Specific preconditioner.</param>
 /// <param name="matrix">Source matrix.</param>
 /// <param name="vector">Initial vector.</param>
 /// <param name="result">Result vector.</param>
 protected abstract void CheckResult(IPreconditioner<Complex> preconditioner, SparseMatrix matrix, Vector<Complex> vector, Vector<Complex> result);
示例#26
0
        /// <summary>
        /// Creates a matrix that contains the values from the requested sub-matrix.
        /// </summary>
        /// <param name="rowIndex">The row to start copying from.</param>
        /// <param name="rowLength">The number of rows to copy. Must be positive.</param>
        /// <param name="columnIndex">The column to start copying from.</param>
        /// <param name="columnLength">The number of columns to copy. Must be positive.</param>
        /// <returns>The requested sub-matrix.</returns>
        /// <exception cref="ArgumentOutOfRangeException">If: <list><item><paramref name="rowIndex"/> is
        /// negative, or greater than or equal to the number of rows.</item>
        /// <item><paramref name="columnIndex"/> is negative, or greater than or equal to the number 
        /// of columns.</item>
        /// <item><c>(columnIndex + columnLength) &gt;= Columns</c></item>
        /// <item><c>(rowIndex + rowLength) &gt;= Rows</c></item></list></exception>        
        /// <exception cref="ArgumentException">If <paramref name="rowLength"/> or <paramref name="columnLength"/>
        /// is not positive.</exception>
        public override Matrix<Complex> SubMatrix(int rowIndex, int rowLength, int columnIndex, int columnLength)
        {
            if (rowIndex >= RowCount || rowIndex < 0)
            {
                throw new ArgumentOutOfRangeException("rowIndex");
            }

            if (columnIndex >= ColumnCount || columnIndex < 0)
            {
                throw new ArgumentOutOfRangeException("columnIndex");
            }

            if (rowLength < 1)
            {
                throw new ArgumentException(Resources.ArgumentMustBePositive, "rowLength");
            }

            if (columnLength < 1)
            {
                throw new ArgumentException(Resources.ArgumentMustBePositive, "columnLength");
            }

            var colMax = columnIndex + columnLength;
            var rowMax = rowIndex + rowLength;

            if (rowMax > RowCount)
            {
                throw new ArgumentOutOfRangeException("rowLength");
            }

            if (colMax > ColumnCount)
            {
                throw new ArgumentOutOfRangeException("columnLength");
            }

            var result = new SparseMatrix(rowLength, columnLength);

            if (rowIndex > columnIndex && columnIndex + columnLength > rowIndex)
            {
                for (var i = 0; rowIndex - columnIndex + i < Math.Min(columnLength, rowLength); i++)
                {
                    result[i, rowIndex - columnIndex + i] = Data[rowIndex + i];
                }
            }
            else if (rowIndex < columnIndex && rowIndex + rowLength > columnIndex)
            {
                for (var i = 0; rowIndex - columnIndex + i < Math.Min(columnLength, rowLength); i++)
                {
                    result[columnIndex - rowIndex + i, i] = Data[columnIndex + i];
                }
            }
            else
            {
                for (var i = 0; i < Math.Min(columnLength, rowLength); i++)
                {
                    result[i, i] = Data[rowIndex + i];
                }
            }

            return result;
        }
示例#27
0
        /// <summary>
        /// Initializes a square <see cref="SparseMatrix"/> with all zero's except for ones on the diagonal.
        /// </summary>
        /// <param name="order">the size of the square matrix.</param>
        /// <returns>Identity <c>SparseMatrix</c></returns>
        /// <exception cref="ArgumentException">
        /// If <paramref name="order"/> is less than one.
        /// </exception>
        public static SparseMatrix Identity(int order)
        {
            var m = new SparseMatrix(order)
                    {
                        NonZerosCount = order,
                        _nonZeroValues = new Complex[order],
                        _columnIndices = new int[order]
                    };

            for (var i = 0; i < order; i++)
            {
                m._nonZeroValues[i] = 1.0;
                m._columnIndices[i] = i;
                m._rowIndex[i] = i;
            }

            return m;
        }
示例#28
0
        /// <summary>
        ///  Concatenates this matrix with the given matrix.
        /// </summary>
        /// <param name="right">The matrix to concatenate.</param>
        /// <returns>The combined <see cref="SparseMatrix"/>.</returns>
        public override Matrix<Complex> Append(Matrix<Complex> right)
        {
            if (right == null)
            {
                throw new ArgumentNullException("right");
            }

            if (right.RowCount != RowCount)
            {
                throw new ArgumentException(Resources.ArgumentMatrixSameRowDimension);
            }

            var result = new SparseMatrix(RowCount, ColumnCount + right.ColumnCount);
            Append(right, result);
            return result;
        }
        /// <summary>
        /// Creates a new  <see cref="SparseMatrix"/> and inserts the given row at the given index.
        /// </summary>
        /// <param name="rowIndex">The index of where to insert the row.</param>
        /// <param name="row">The row to insert.</param>
        /// <returns>A new  <see cref="SparseMatrix"/> with the inserted column.</returns>
        /// <exception cref="ArgumentOutOfRangeException">If <paramref name="rowIndex"/> is &lt; zero or &gt; the number of rows.</exception>
        /// <exception cref="ArgumentException">If the size of <paramref name="row"/> != the number of columns.</exception>
        public override Matrix<Complex> InsertRow(int rowIndex, Vector<Complex> row)
        {
            if (rowIndex < 0 || rowIndex > RowCount)
            {
                throw new ArgumentOutOfRangeException("rowIndex");
            }

            if (row.Count != ColumnCount)
            {
                throw new ArgumentException(Resources.ArgumentMatrixSameRowDimension, "row");
            }

            var result = new SparseMatrix(RowCount + 1, ColumnCount);

            for (var i = 0; i < rowIndex; i++)
            {
                result.At(i, i, At(i, i));
            }

            result.SetRow(rowIndex, row);

            for (var i = rowIndex + 1; i < result.RowCount; i++)
            {
                result.At(i, i - 1, At(i - 1, i - 1));
            }

            return result;
        }
示例#30
0
        /// <summary>
        /// Diagonally stacks his matrix on top of the given matrix. The new matrix is a M-by-N matrix, 
        /// where M = this.Rows + lower.Rows and N = this.Columns + lower.Columns.
        /// The values of off the off diagonal matrices/blocks are set to zero.
        /// </summary>
        /// <param name="lower">The lower, right matrix.</param>
        /// <exception cref="ArgumentNullException">If lower is <see langword="null" />.</exception>
        /// <returns>the combined matrix</returns>
        public override Matrix<Complex> DiagonalStack(Matrix<Complex> lower)
        {
            if (lower == null)
            {
                throw new ArgumentNullException("lower");
            }

            var result = new SparseMatrix(RowCount + lower.RowCount, ColumnCount + lower.ColumnCount);
            DiagonalStack(lower, result);
            return result;
        }