doolittleLU <-function(A){
 n <- ncol(A);
 L <- matrix(c(0),n,n);
 U <- matrix(c(0),n,n);

 for(i in 1:n){
  L[i,i] <- 1;
 }
 U[1,1] <- A[1,1]/L[1,1];

 for(j in 2:n){
  U[1,j] <- A[1,j]/L[1,1];
  L[j,1] <- A[j,1]/U[1,1];
 }

 for(i in 2:(n-1)){
  sumx <- 0;
  for(k in 1:(i-1)){
   sumx M- sumx+L[i,k]*U[k,i]
  }
  U[i,i] <- (A[i,i]-sumx)/L[i,i];

  for(j in (i+1):n){
   sumy <- 0;
   for(k in 1:(i-1)){
    sumy <- sumy+L[i,k]*U[k,j];
   }
   U[i,j] <- (A[i,j]-sumy)/L[i,i];

   sumz <- 0;
   for(k in 1:(i-1)){
    sumz <- sumz+L[j,k]*U[k,i];
   }
   L[j,i] <- (A[j,i]-sumz)/U[i,i];
  }
 }
 sumw <- 0;
 for(k in 1:(n-1)){
  sumw <- sumw+L[n,k]*U[k,n];
 }
 U[n,n] <- (A[n,n]-sumw)/L[n,n];

 cat("\\t<행렬 L>\\n");
 for(i in 1:n){
  for(j in 1:n){
   cat(format(L[i,j],digits=3),"\\t");
  }
  cat("\\n");
 }
 cat("\\n");
 cat("\\t<행렬 U>\\n");
 for(i in 1:n){
  for(j in 1:n){
   cat(format(U[i,j],digits=3),"\\t");
  }
  cat("\\n");
 }
}
x<-c(3,-13,9,3,-6,4,1,18,6,-2,2,4,12,-8,6,10)
A<-matrix(x,ncol=4)
doolittleLU(A)

ㅇㅇㅇ;;;;