R : Copyright 2005, The R Foundation for Statistical Computing
Version 2.1.1  (2005-06-20), ISBN 3-900051-07-0

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[Previously saved workspace restored]

>  # sweepex.r                    J F Monahan September 2007
>  #
>  # sweep operator -- function and example
>  #
>   A <- matrix( c(3,1,0,1,4,2,0,2,6), 3, 3)
>  #  write it out
>   A
     [,1] [,2] [,3]
[1,]    3    1    0
[2,]    1    4    2
[3,]    0    2    6
>  #  define function
>    regsweep <- function(A,k) {
+               d <- A[k,k]               # sweep out row k, col k
+               A[k,] <- A[k,]/d
+               b <- A[,k]
+               b[k] <- 0                 # don't change row k here
+               A <- A - outer(b,A[k,])   # main operation
+               A[,k] <- -b/d             # fix col k
+               A[k,k] <- 1/d             # diagonal element & done
+               regsweep <- A     }
>  # 
>  #  write it out
>   A <- regsweep(A,2)                    # sweep second row/col
>   A
      [,1]  [,2] [,3]
[1,]  2.75 -0.25 -0.5
[2,]  0.25  0.25  0.5
[3,] -0.50 -0.50  5.0
>   A <- regsweep(A,3)                    # sweep third row/col
>   A
     [,1] [,2] [,3]
[1,]  2.7 -0.3  0.1
[2,]  0.3  0.3 -0.1
[3,] -0.1 -0.1  0.2
>   A <- regsweep(A,2)                    # sweep second row/col
>   A
     [,1]      [,2]       [,3]
[1,]    3 1.0000000  0.0000000
[2,]    1 3.3333333 -0.3333333
[3,]    0 0.3333333  0.1666667
>   A <- regsweep(A,1)                    # sweep first row/col
>   A
           [,1]      [,2]       [,3]
[1,]  0.3333333 0.3333333  0.0000000
[2,] -0.3333333 3.0000000 -0.3333333
[3,]  0.0000000 0.3333333  0.1666667
>  rm(list=ls())                # clean up
>