逆行列

25-164248.cpp

#include<iostream>
#include<iomanip>

int main(int argc, char *argv[]){
  int n;
  double input;
  std::cout << "n次の正方行列? n:";
  std::cin >> n;
  double a[n][n];
  double e[n][n];
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      std::cout << i+1 << "行" << j+1 << "列目:";
      std::cin >> input;
      a[i][j] = input;
      if(i==j){
	e[i][j]=1.0;
      }else{
	e[i][j]=0.0;
      }
    }
  }

  double buf;
  for(int i=0;i<n;i++){
    buf = 1/a[i][i];
    for(int j=0;j<n;j++){
      a[i][j] = a[i][j] * buf;
      e[i][j] = e[i][j] * buf;
    }

    for(int j=0;j<n;j++){
      if(i!=j){
	buf = a[j][i];
	for(int k=0;k<n;k++){
	  a[j][k] = a[j][k] - a[i][k]*buf;
	  e[j][k] = e[j][k] - e[i][k]*buf;
	}
      }
    }
  }

  std::cout << std::fixed << std::setprecision(4);

  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      std::cout << e[i][j] << " ";
    }
    std::cout << std::endl;
  }

  return 0;
}