Question

我正在编写一个方法来计算包含双精度的矩阵（这里是一个二维数组）的行列式。这是我写的：

/// <summary>
/// Checks to see if a matrix is square, and then computes its determinant
/// </summary>
/// <returns></returns>
public double Determinant()
{
    // Check to make sure the matrix is square.  Only square matrices 
    // have determinants.
    if (!this.isSquare())
    {
        throw new Exception("The matrix does not have a determinant");
    }

    // Check to see if the matrix has dimensions 1x1.  
    // The determinant of a 1x1 matrix is equal to the value stored at (0,0).
    if (this.NumberOfRows == 1)
    {
        return this.GetElement(0, 0);
    }

    double determinant = 0;

    // Loop through the top row of the matrix.
    for (int columnIndex = 0; columnIndex < this.NumberOfColumns; columnIndex++)
    {
        Matrix cofactor = new Matrix(this.NumberOfRows - 1, this.NumberOfColumns - 1);

        //fill cofactor
        //I dont Know what to do here?


        determinant += this.GetElement(1, columnIndex) * cofactor.Determinant();
    }

    return determinant;
}

我缺少的是应该在第fill cofactor行。

有人可以建议我应该在那里做什么吗？基本上，从原始矩阵向辅助因子添加元素而忽略矩阵中当前位置的行或列中出现的那些元素的最佳方法是什么？

Answer 1

您只需删除第一个（第0个）行和您不想要的列。以下内容对您有用：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        /// <summary>
        /// Helper to show array.
        /// </summary>
        /// <param name="mat"></param>
        static void ShowArray(double[,] mat)
        {
            int ubound = mat.GetUpperBound(0);

            for (int row = 0; row <= ubound; row++)
            {
                for (int col = 0; col <= ubound; col++)
                {
                    Console.Write(string.Format("{0,2} ", mat[col, row]));
                }
                Console.WriteLine();
            };

            Console.WriteLine();

        }

        /// <summary>
        /// Get an array without the zeroth row and without a specified column.
        /// </summary>
        /// <param name="mat">The square array to remove items from.</param>
        /// <param name="knockoutCol">The column to eliminate.</param>
        /// <returns>A square array of size one less than the input array.</returns>
        static double[,] SubMatrix(double[,] mat, int knockoutCol)
        {
            if (mat.GetUpperBound(0) != mat.GetUpperBound(1))
            {
                throw new ArgumentException("Array is not square.");
            }

            int ubound = mat.GetUpperBound(0);
            double[,] m = new double[ubound, ubound];

            int mCol = 0;
            int mRow = 0;

            for (int row = 1; row <= ubound; row++)
            {
                mCol = 0;
                for (int col = 0; col <= ubound; col++)
                {
                    if (col == knockoutCol)
                    {
                        continue;
                    }
                    else
                    {
                        m[mCol, mRow] = mat[col, row];
                        mCol += 1;
                    }
                }
                mRow += 1;

            };

            return m;
        }

        static void Main(string[] args)
        {
            int arraySize = 4;
            double[,] mat = new double[arraySize, arraySize];
            int ubound = mat.GetUpperBound(0);

            // Initialise array for inspection.
            for (int row = 0; row <= ubound; row++)
            {
                for (int col = 0; col <= ubound; col++)
                {
                    mat[col, row] = (arraySize * row) + col;
                }
            };

            ShowArray(mat);

            ShowArray(SubMatrix(mat, 0));
            ShowArray(SubMatrix(mat, 1));
            ShowArray(SubMatrix(mat, 2));

            Console.ReadLine();

        }
    }
}

输出：

 0  1  2  3
 4  5  6  7
 8  9 10 11
12 13 14 15

 5  6  7
 9 10 11
13 14 15

 4  6  7
 8 10 11
12 14 15

 4  5  7
 8  9 11
12 13 15

如果我在开始时更仔细地考虑它，我可能已经交换了行和列。

计算矩阵行列式的下一步

1 个答案: