Does the following do what you want:
> vl.mat <- matrix(0,4,4)
> i34 <- 3:4
> vl.mat[i34,i34] <- 100
> vl.mat
[,1] [,2] [,3] [,4]
[1,] 0 0 0 0
[2,] 0 0 0 0
[3,] 0 0 100 100
[4,] 0 0 100 100
>
spencer graves
Doran, Harold wrote:
Dear List:
I am having some difficulty constructing a matrix that must take a
specific form. The matrix must be have a lower block of non-zero values
and the rest must all be zero. For example, if I am building an n X n
matrix, then the first n/2 rows need to be zero and the first n/2
columns must remain as zero with all other elements having a non-zero
value that I specify.
For example, assume I start with the following 4 x 4 matrix:
vl.mat <- matrix(0,4,4)
[,1] [,2] [,3] [,4]
[1,] 0 0 0 0
[2,] 0 0 0 0
[3,] 0 0 0 0
[4,] 0 0 0 0
I need for the for the first two columns (4/2) to remain as zero and the
first two rows (4/2) to remain as zeros. But I need for the bottom block
to include some values that I specify.
[,1] [,2] [,3] [,4]
[1,] 0 0 0 0
[2,] 0 0 0 0
[3,] 0 0 100 100
[4,] 0 0 100 100
I know that if I use the following I can build a matrix with values
along the diagonals where I need them, but I need for the lower block of
off-diagonals to also be the same value.
vl.mat <- matrix(0,4,4)
vl.mat[(col(vl.mat)%%4 == row(vl.mat)%%4)&col(vl.mat)%%4 !=1
&col(vl.mat)%%4 !=2 ] <- 100
Can anyone offer a suggestion? Thank you.
-Harold
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