spdiags {crqa}

Extract diagonal matrices

Description

Extracts all nonzero diagonals from the m-by-n matrix A. B is a min(m,n)-by-p matrix whose columns are the p nonzero diagonals of A.

Usage

 spdiags(A) 

Arguments

A

An m-by-n matrix with nonzero elements located on p diagonals.

Details

Compared to the original Matlab implementation: 1) it does not handle the case with more than one input, and 2) (m > n) matrices give the B matrix columns in a different order, but the d vector of indices will also be changed accordingly, so the set of columns is OK, just ordered differently

Value

B

A min(m,n)-by-p matrix, usually (but not necessarily) full, whose columns are the diagonals of A.

d

A vector of length p whose integer components specify the diagonals in A.

Note

For computational efficiency spdiags is actually computed using a Fortan implementation (jspd.f)

Author(s)

John C. Nash ([e-mail])

Examples

dta <- c(0, 5, 0, 10, 0, 0, 0, 0, 6, 0, 11, 0, 3, 0, 0,
7, 0, 12, 1, 4, 0, 0, 8, 0, 0, 2, 5, 0, 0, 9)

A1 <- matrix(dta, nrow=5, ncol=6, byrow=TRUE)

print(A1)
res1 <- spdiags(A1)
print(res1)