polyMatrix (version 0.3.1)

diag: Extracts the diagonal of a polyMatrix, or constructs a diagonal polyMatrix

Description

If the input is a polyMatrix then the output is its diagonal. If the input is a vector then the output is a diagonal matrix.

Usage

diag(x, nrow=NULL, ncol=NULL, names=NULL, type=CLASS_LIST, ...)

Arguments

x

input material for the diagonal matrix

nrow

number of rows in the output object

ncol

number of columns in the output object

names

(when 'x' is a matrix) logical indicating if the resulting vector, the diagonal of 'x', should inherit 'names' from 'dimnames(x)' if available.

type

the required form and class of the result: CLASS_LIST or CLASS_MATRIX

…

...

Value

The returned value is a

list

class object, when it extracts the diagonal from a polyMatrix, and the value of type isn't 'polyMatrix'.

polyMatrix

class object, when builds a matrix from the given diagonal or when returns the diagonal of a polyMatrix, and the type="polyMatrix".

Details

The diag has two different applications. When the class of the first input parameter is

• 'list', then returns a polyMatrix with the given diagonal and zero off-diagonal entries.

• 'polyMatrix', then extracts the diagonal.

Note. In the first case the elements of the list must be polynomial class objects. In the second case the result is a list or polyMatrix class object determined by the value of the type parameter.

See Also

polyMatrix-package.

Examples

# NOT RUN {
# ---
# case of real matrices

m<-matrix(1:12,3,4)
m
diag(m) # first type usage

v<-c(1,5,9) # second type usage
diag(v)
diag(v,4)
diag(v,4,2)
diag(v,ncol=4)

# ---
# case of polynomial matrices

# first kind usage: catch the diagonal elements

px<-polyMgen.d(3,3,rawData=ch2pn(
     c("-3 + z^2","2 + 4*z","-z^2",
       "1","2","3 + z",
       "2*z","0","2 - 3*z"),"z"),byrow=TRUE)
class(px) # "polyMdlist" "polyMatrix"
px

w<-diag(px) # the default: type="list"
class(w) # "list"
# List of 3
# $ :Class 'polynomial'  num [1:3] -3 0 1
# $ :Class 'polynomial'  num 2
# $ :Class 'polynomial'  num [1:2] 2 -3
w

w<-diag(px,type="polyMatrix")
class(w) # "polyMdlist" "polyMatrix"
w

# second kind usage: compose a diagonal polyMatrix

ci<-c(4,1,3,2)
v<-vector("list",length(ci))
for(i in 1:length(ci))
  v[[i]]<-polynom::polynomial(c(rep(0,ci[i]),1))
class(v) # "list"
v

diag(v)
diag(v,4)
diag(v,3)
diag(v,5)
diag(v,3,5)

pd<-diag(v,4,5)
class(pd) # "polyMdlist" "polyMatrix"
pd

# clean up
# rm(ci, i, m, pd, px, v, w)

# }