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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