package com.yang.matrix;
public class TestMatrix {
public static void main(String[] args) {
// 测试数据
// double[][] a={{0.2368,0.2471,0.2568,1.2671},
// {1.1161,0.1254,0.1397,0.149},
// {0.1582,1.1675,0.1768,0.1871},
// {0.1968,0.2071,1.2168,0.2271}};
double[][] a={{1,3,1},
{2,1,1},
{2,2,1}
};
double[][] b={{1,3,1},
{2,1,1},
{2,2,1}
};
double[][] c= new double[3][3];
TestMatrix tm=new TestMatrix();
tm.Mrinv(a, 3);
//验证 A*A-1=E
tm.Mrcheng(a,b,c,3,3,3);
tm.PrintMatrix(c, 3);
}
public static void PrintMatrix(double[][] a, int n){
for(int i=0;i<n;i++){
for(int j=0;j<n;j++)
{
System.out.print(a[i][j]+" ");
}
System.out.println();
}
}
////////////////////////////////////////////////////////////////////////
//函数：Mrinv
//功能：求矩阵的逆
//参数：n---整数，矩阵的阶数
//a---Double型n*n二维数组，开始时为原矩阵，返回时为逆矩阵
////////////////////////////////////////////////////////////////////////
public static void Mrinv(double[][] a, int n) {
int i, j, row, col, k;
double max, temp;
int[] p = new int[n];
double[][] b = new double[n][n];
for (i = 0; i < n; i++) {
p[i] = i;
b[i][i] = 1;
}
for (k = 0; k < n; k++) {
// 找主元
max = 0;
row = col = i;
for (i = k; i < n; i++)
for (j = k; j < n; j++) {
temp = Math.abs(b[i][j]);
if (max < temp) {
max = temp;
row = i;
col = j;
}
}
// 交换行列，将主元调整到 k 行 k 列上
if (row != k) {
for (j = 0; j < n; j++) {
temp = a[row][j];
a[row][j] = a[k][j];
a[k][j] = temp;
temp = b[row][j];
b[row][j] = b[k][j];
b[k][j] = temp;
}
i = p[row];
p[row] = p[k];
p[k] = i;
}
if (col != k) {
for (i = 0; i < n; i++) {
temp = a[i][col];
a[i][col] = a[i][k];
a[i][k] = temp;
}
}
// 处理
for (j = k + 1; j < n; j++)
a[k][j] /= a[k][k];
for (j = 0; j < n; j++)
b[k][j] /= a[k][k];
a[k][k] = 1;
for (j = k + 1; j < n; j++) {
for (i = 0; i < k; i++)
a[i][j] -= a[i][k] * a[k][j];
for (i = k + 1; i < n; i++)
a[i][j] -= a[i][k] * a[k][j];
}
for (j = 0; j < n; j++) {
for (i = 0; i < k; i++)
b[i][j] -= a[i][k] * b[k][j];
for (i = k + 1; i < n; i++)
b[i][j] -= a[i][k] * b[k][j];
}
for (i = 0; i < k; i++)
a[i][k] = 0;
a[k][k] = 1;
}
// 恢复行列次序；
for (j = 0; j < n; j++)
for (i = 0; i < n; i++)
a[p[i]][j] = b[i][j];
}
//矩阵乘法
public void Mrcheng(double[][] a,double[][] b,double[][]c,int m,int n,int l)
{
double[][] d=new double[m][l];
//使用中间变量d,是防止c=a或c=b的情形下计算出错
int i,j,k;
for(i=0;i<m;i++)
for(j=0;j<l;j++)
{
d[i][j]=0;
for(k=0;k<n;k++)
d[i][j]+=a[i][k]*b[k][j];
}
for(i=0;i<m;i++)
for(j=0;j<l;j++)
c[i][j]=d[i][j];
}
}
