static void Main(string[] args)
{
#region 1. Declaring matrices
// 1.1 Using standard .NET declaration
double[,] A =
{
{ 1, 2, 3 },
{ 6, 2, 0 },
{ 0, 0, 1 }
};
double[,] B =
{
{ 2, 0, 0 },
{ 0, 2, 0 },
{ 0, 0, 2 }
};
{
// 1.2 Using Accord extension methods
double[,] Bi = Matrix.Identity(3).Multiply(2);
double[,] Bj = Matrix.Diagonal(3, 2.0); // both are equal to B
// 1.2 Using Accord extension methods with implicit typing
var I = Matrix.Identity(3);
}
#endregion
#region 2. Matrix Operations
{
// 2.1 Addition
var C = A.Add(B);
// 2.2 Subtraction
var D = A.Subtract(B);
// 2.3 Multiplication
{
// 2.3.1 By a scalar
var halfM = A.Multiply(0.5);
// 2.3.2 By a vector
double[] m = A.Multiply(new double[] { 1, 2, 3 });
// 2.3.3 By a matrix
var M = A.Multiply(B);
// 2.4 Transposing
var At = A.Transpose();
}
}
// 2.5 Elementwise operations
// 2.5.1 Elementwise multiplication
A.ElementwiseMultiply(B); // A.*B
// 2.5.1 Elementwise division
A.ElementwiseDivide(B); // A./B
#endregion
#region 3. Matrix characteristics
{
// 3.1 Calculating the determinant
double det = A.Determinant();
// 3.2 Calculating the trace
double tr = A.Trace();
// 3.3 Computing the sum vector
{
double[] sumVector = A.Sum();
// 3.3.1 Computing the total sum of elements
double sum = sumVector.Sum();
// 3.3.2 Computing the sum along the rows
sumVector = A.Sum(0); // Equivalent to Octave's sum(A, 1)
// 3.3.2 Computing the sum along the columns
sumVector = A.Sum(1); // Equivalent to Octave's sum(A, 2)
}
}
#endregion
#region 4. Linear Algebra
{
// 4.1 Computing the inverse
var invA = A.Inverse();
// 4.2 Computing the pseudo-inverse
var pinvA = A.PseudoInverse();
// 4.3 Solving a linear system (Ax = B)
var x = A.Solve(B);
}
#endregion
#region 5. Special operators
{
// 5.1 Finding the indices of elements
double[] v = { 5, 2, 2, 7, 1, 0 };
int[] idx = v.Find(e => e > 2); // finding the index of every element in v higher than 2.
// 5.2 Selecting elements by index
double[] u = v.Submatrix(idx); // u is { 5, 7 }
// 5.3 Converting between different matrix representations
double[][] jaggedA = A.ToArray(); // from multidimensional to jagged array
// 5.4 Extracting a column or row from the matrix
double[] a = A.GetColumn(0); // retrieves the first column
double[] b = B.GetRow(1); // retrieves the second row
// 5.5 Taking the absolute of a matrix
var absA = A.Abs();
// 5.6 Applying some function to every element
var newv = v.Apply(e => e + 1);
}
#endregion
#region 7. Vector operations
{
double[] u = { 1, 2, 3 };
double[] v = { 4, 5, 6 };
var w1 = u.InnerProduct(v);
var w2 = u.OuterProduct(v);
var w3 = u.CartesianProduct(v);
double[] m = { 1, 2, 3, 4 };
double[,] M = Matrix.Reshape(m, 2, 2);
}
#endregion
#region Decompositions
{
// Singular value decomposition
{
SingularValueDecomposition svd = new SingularValueDecomposition(A);
var U = svd.LeftSingularVectors;
var S = svd.Diagonal;
var V = svd.RightSingularVectors;
}
// or (please see documentation for details)
{
SingularValueDecomposition svd = new SingularValueDecomposition(A.Transpose());
var U = svd.RightSingularVectors;
var S = svd.Diagonal;
var V = svd.LeftSingularVectors;
}
// Eigenvalue decomposition
{
EigenvalueDecomposition eig = new EigenvalueDecomposition(A);
var V = eig.Eigenvectors;
var D = eig.DiagonalMatrix;
}
// QR decomposition
{
QrDecomposition qr = new QrDecomposition(A);
var Q = qr.OrthogonalFactor;
var R = qr.UpperTriangularFactor;
}
// Cholesky decomposition
{
CholeskyDecomposition chol = new CholeskyDecomposition(A);
var R = chol.LeftTriangularFactor;
}
// LU decomposition
{
LuDecomposition lu = new LuDecomposition(A);
var L = lu.LowerTriangularFactor;
var U = lu.UpperTriangularFactor;
}
}
#endregion
}
