/// <summary>
/// Multiplication of two rows from two matrices respectively.
/// </summary>
/// <param name="matrix"></param>
/// <param name="row"></param>
/// <param name="other"></param>
/// <param name="otherRow"></param>
/// <returns></returns>
public static double RowMultiplication(this DenseMatrix <double> matrix, int row, DenseMatrix <double> other, int otherRow)
{
double sum = 0.0;
for (int i = 0; i < matrix.NumberOfColumns; i++)
{
sum += matrix[row, i] * other[otherRow, i];
}
return(sum);
}
/// <summary>
/// Inverse of a matrix.
/// </summary>
/// <param name="matrix">The inversed matrix</param>
/// <returns></returns>
public static DenseMatrix <double> Inverse(this DenseMatrix <double> matrix)
{
int m = matrix.NumberOfRows;
int n = matrix.NumberOfColumns;
double[,] array = new double[2 * m + 1, 2 * n + 1];
for (int k = 0; k < 2 * m + 1; k++) // Initialize
{
for (int t = 0; t < 2 * n + 1; t++)
{
array[k, t] = 0.00000000;
}
}
for (int i = 0; i < m; i++)
{
for (int j = 0; j < n; j++)
{
array[i, j] = matrix[i, j];
}
}
for (int k = 0; k < m; k++)
{
for (int t = n; t <= 2 * n; t++)
{
if ((t - k) == m)
{
array[k, t] = 1.0;
}
else
{
array[k, t] = 0;
}
}
}
//得到逆矩阵
for (int k = 0; k < m; k++)
{
if (array[k, k] != 1)
{
double bs = array[k, k];
array[k, k] = 1;
for (int p = k + 1; p < 2 * n; p++)
{
array[k, p] /= bs;
}
}
for (int q = 0; q < m; q++)
{
if (q != k)
{
double bs = array[q, k];
for (int p = 0; p < 2 * n; p++)
{
array[q, p] -= bs * array[k, p];
}
}
else
{
continue;
}
}
}
DenseMatrix <double> NI = new DenseMatrix <double>(m, n);
for (int x = 0; x < m; x++)
{
for (int y = n; y < 2 * n; y++)
{
NI[x, y - n] = array[x, y];
}
}
return(NI);
}
