public Matrix GetCofactor()
{
// https://www.mathwords.com/c/cofactor_matrix.htm
decimal[,] cofactor = new decimal[Height, Width];
for (int rowIndex = 0; rowIndex < Height; rowIndex++)
{
for (int columnIndex = 0; columnIndex < Width; columnIndex++)
{
cofactor[rowIndex, columnIndex] = new Cofactor(
this,
rowIndex,
columnIndex).GetDeterminant();
}
}
return(new Matrix(cofactor));
}
private static decimal GetDeterminant(
Matrix matrix)
{
// you can only get a determinant from a square matrix
// using expansion by cofactors
// https://www.mathwords.com/e/expansion_by_cofactors.htm
// look for 2x2 matrix
if (matrix.Height == 2)
{
return(GetDeterminant(
matrix[0, 0],
matrix[1, 0],
matrix[0, 1],
matrix[1, 1]));
}
else
{
decimal determinant = 0;
for (int columnIndex = 0; columnIndex < matrix.Width; columnIndex++)
{
Cofactor cofactor = new Cofactor(
matrix,
0,
columnIndex);
determinant +=
matrix[0, columnIndex] *
cofactor.GetDeterminant();
}
return(determinant);
}
}
