HP MLIB User's Guide Vol. 1 7th Ed.

432 HP MLIB User’s Guide
What you need to know to use these subprograms
Table 4-15 SKY Format Matrix
Block entry formats
All block entry formats can be used to represent matrices with fixed square
block size. The Variable Block Compressed Sparse Row format can also be used
for matrices with variable block sizes.
BCO - Block coordinate. Given a sparse block matrix A formed by mb-by-kb
square blocks of size lb-by-lb each, the block coordinate format represents the
bnnz nonzero block entries using the same variables as in the COO format.
Each nonzero dense block is stored in column major order. Three arrays are
required for the BCO representation:
• val( lb, lb,*) - Scalar matrix of dimension lb-by-lb-by-bnnz containing the
nonzero lb-by-lb blocks.
• bindx(*) - Integer array of length bnnz containing block row indices such
that bindx(i) corresponds to the block row index of the matrix block val( :, :,
i).
• bjndx(*) - Integer array of length bnnz containing block column indices such
that bjndx(i) corresponds to the block column index of val( :, :, i).
Consider, for example, the 4 x 6 matrix:
Table 4-16 4 x 6 Matrix
val= 11 21 22 32 33 42 0 44 51 0 0 54 55
pntr= 1246914
11 12 0 0 15 16
21 22 0 0 25 26
0 0 33 0 35 36
0 0 43 44 0 46