[R] How to define new matrix based on an elementary row operation in a single step?

[Cheng Peng]

Sorry for possible misunderstanding:

I want to define a matrix (B) based on an existing matrix (A) in a single
step and keep A unchanged:
 
> #Existing matrix
> A=matrix(1:16,ncol=4)
> A
     [,1] [,2] [,3] [,4]
[1,]    1    5    9   13
[2,]    2    6   10   14
[3,]    3    7   11   15
[4,]    4    8   12   16
> # New matrix B is defined to be the submatrix after row1 and column1 are
> deleted.
> B=A[-1,-1]    # this single step deletes row1 nad column 1 and assigns the
> name to the resulting submatrix.
> B                 # check the new matrix B
     [,1] [,2] [,3]
[1,]    6   10   14
[2,]    7   11   15
[3,]    8   12   16
> A                 # check the original matrix A
     [,1] [,2] [,3] [,4]
[1,]    1    5    9   13
[2,]    2    6   10   14
[3,]    3    7   11   15
[4,]    4    8   12   16


Question: How can I do define a new matrix (D) by adding 2*row1 to row3 in A
in a single step as what was done in the above example?

If you do:  A[3,]=2*A[1,]+A[3,],  the new A is not the original A; if you
D=A first, then D[3,]=2*D[1,]+D[3,], you used two step!

Hope this clarifies my original question. Thanks again.





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