Help for package multipol

Type:

Package

Title:

Multivariate Polynomials

Version:

1.0-9

Depends:

abind

Suggests:

polynom,testthat

Maintainer:

Robin K. S. Hankin <hankin.robin@gmail.com>

Description:

Various utilities to manipulate multivariate polynomials. The package is almost completely superceded by the 'spray' and 'mvp' packages, which are much more efficient.

License:

GPL-2 | GPL-3 [expanded from: GPL]

NeedsCompilation:

Repository:

CRAN

Packaged:

2023-08-20 05:03:52 UTC; rhankin

Author:

Robin K. S. Hankin

[aut, cre]

Date/Publication:

2023-08-21 08:02:35 UTC

Multivariate polynomials

Description

Various tools to manipulate and combine multivariate polynomials

Details

Multidimensional arrays are interpreted in a natural way as multivariate polynomials.

Taking a matrix a as an example, because this has two dimensions it may be viewed as a bivariate polynomial with a[i,j] being the coefficient of x^iy^j. Note the off-by-one issue; see ?Extract.

Multivariate polynomials of arbitrary arity are a straightforward generalization using appropriately dimensioned arrays.

Arithmetic operations “+”,“-”, “*”, “^” operate as though their arguments are multivariate polynomials.

Even quite small multipols are computationally intense; many coefficients have to be calculated and each is the sum of many terms.

The package is almost completely superceded by the spray and mvp packages, which use a sparse array system for efficiency.

Author(s)

Maintainer: Robin K. S. Hankin <hankin.robin@gmail.com>

Examples


ones(2)*linear(c(1,-1))                             # x^2-y^2
ones(2)*(ones(2,2)-uni(2))                          # x^3+y^3


a <- as.multipol(matrix(1:12,3,4))
a

a[1,1] <- 11

f <- as.function(a*a)

f(c(1,pi))

Extract or Replace Parts of a multipol

Description

Extract or replace subsets of multipols

Usage

          ## S3 method for class 'multipol'
x[...]
          ## S3 replacement method for class 'multipol'
x[...] <- value

Arguments

x

A multipol

...

Indices to replace. Offset zero! See details section

value

replacement value

Details

Extraction and replacement operate with offset zero (using functions taken from the Oarray package); see the examples section. This is so that the index matches the power required (there is an off-by-one issue. The first element corresponds to the zeroth power. One wants index i to extract/replace the i-th power and in particular one wants index 0 to extract/replace the zeroth power).

Replacement operators return a multipol. Extraction returns an array. This is because it is often not clear exactly what multipol is desired from an extraction operation (it is also consistent with Oarray's behaviour).

Author(s)

Original code taken from the Oarray package by Jonty Rougier

References

Jonathan Rougier (2007). Oarray: Arrays with arbitrary offsets. R package version 1.4-2.

Examples

a <- as.multipol(matrix(1,4,6))
a[2,2] <- 100
a                  # coefficient of x1^2.x2^2 is 100

a[1:2,1:2]         # a matrix.  Note this corresponds to first and second powers
                   # not zeroth and first (what multipol would you want here?)

a[2,2]             # 100 to match the "a[2,2] <- 100" assignment above

Arithmetic ops group methods for multipols

Description

Allows arithmetic operators to be used for multivariate polynomials such as addition, multiplication, and integer powers.

Usage

## S3 method for class 'multipol'
Ops(e1, e2 = NULL)
mprod(...,  trim = TRUE , maxorder=NULL)
mplus(...,  trim = TRUE , maxorder=NULL)
 mneg(a,    trim = TRUE , maxorder=NULL)
  mps(a, b, trim = TRUE , maxorder=NULL)
 mpow(a, n, trim = TRUE , maxorder=NULL)

Arguments

e1, e2, a

Multipols; scalars coerced

b

Scalar

n

Integer power

...

Multipols

trim

Boolean, with default TRUE meaning to return a trim()-ed multipol and FALSE meaning not to trim

maxorder

Numeric vector indicating maximum orders of the output [that is, the highest power retained in the multivariate Taylor expansion about rep(0,d)]. Length-one input is recycled to length d; default value of NULL means to return the full result. More details given under taylor()

Details

The function Ops.multipol() passes unary and binary arithmetic operators (“+”, “-”, “*”, and “^”) to the appropriate specialist function.

In multipol.R, these specialist functions all have formal names such as .multipol.prod.scalar() which follow a rigorous pattern; they are not intended for the end user. They are not exported from the namespace as they begin with a dot.

Five conveniently-named functions are provided in the package for the end-user; these offer greater control than the arithmetic command-line operations in that arguments trim or maxorder may be set. They are:

mprod() for products,
mplus() for addition,
mneg() for the negative,
mps() for adding a scalar,
mpow() for powers.

Addition and multiplication of multivariate polynomials is commutative and associative, to machine precision.

Author(s)

Robin K. S. Hankin

Examples

a <- as.multipol(matrix(1,4,5))
100+a

f <- as.function(a+1i)
f(5:6)


b <- as.multipol(array(rnorm(12),c(2,3,2)))

f1 <- as.function(b)
f2 <- as.function(b*b)
f3 <- as.function(b^3)    # could have said b*b*b

x <- c(1,pi,exp(1))

f1(x)^2 - f2(x)    #should be zero
f1(x)^3 - f3(x)    #should be zero

x1 <- as.multipol(matrix(1:10,ncol=2))
x2 <- as.multipol(matrix(1:10,nrow=2))
x1+x2

Coerce multipols to arrays

Description

Coerce multipols to arrays; unclass

Usage

## S3 method for class 'multipol'
as.array(x, ...)

Arguments

x

multipol

...

Further arguments passed to NextMethod()

Author(s)

Robin K. S. Hankin

Examples

a <- as.multipol(matrix(1,2,2))
as.array(a)

Coerce a multipol to a function

Description

Coerce a multipol to a function using environments

Usage

## S3 method for class 'multipol'
as.function(x, ...)

Arguments

x

A multipol

...

Further arguments, currently ignored

Author(s)

Robin K. S. Hankin

Examples

a <- as.multipol(array (1:12, c(2,3,2)))

f1 <- as.function(a)
f2 <- as.function(a*a)

x <- matrix(rnorm(15),ncol=3)

f1(x)^2 - f2(x)   #should be zero  [non-trivial!]

Various useful multivariate polynomials

Description

Various useful multivariate polynomials such as homogeneous polynomials, linear polynomials, etc

Usage

constant(d)
product(x)
homog(d, n = d, value = 1)
linear(x, power = 1)
lone(d,x)
single(d, e, power = 1)
uni(d)
zero(d)

Arguments

d

Integer giving the dimensionality (arity) of the result

x

A vector of integers

n, e, power

Integers

value

Value for linear multivariate polynomial

Details

In the following, all multipols have their nonzero entries 1 unless otherwise stated.

Function constant(d) returns the constant multivariate polynomial of arity d
Function product(x) returns a multipol of arity length(x) where all(dim(product(x))==x) with all zero entries except the one corresponding to \prod_{i=1}^d {x_i}^{x[i]}
Function homog(d,n) returns the homogeneous multipol of arity d and power n. The coeffients are set to value (default 1); standard recycling is used
Function linear(x) returns a multipol of arity length(x) which is linear in all its arguments and whose coefficients are the elements of x. Argument power returns an equivalent multipol linear in x^power
Function lone(d,x) returns a multipol of arity d that is a product of variables x[i]
Function single(d,e,power) returns a multipol of arity d with a single nonzero entry corresponding to dimension e raised to the power power
Function uni(d) returns x1*x2*...*xd [it is a convenience wrapper for product(rep(1,d))]
Function zero(d) returns the zero multipol of arity d [it is a convenience wrapper for 0*constant(d)]
Function ones(d) returns x1+x2+...+xd [it is a convenience wrapper for linear(rep(1,d))]

Note

In many ways, the functions documented in this section are an adverisement for the inefficiency of dealing with multipols using arrays: sparse arrays would be the natural solution.

Author(s)

Robin K. S. Hankin

Examples


product(c(1,2,5))     #   x * y^2 * z^5
uni(3)                #   xyz
single(3,1)           #   x
single(3,2)           #   y
single(3,3)           #   z
single(3,1,6)         #   x^6        
single(3,2,6)         #   y^6
lone(3,1:2)           #   xy
lone(3,c(1,3))        #   xz
linear(c(1,2,5))      #   x + 2y + 5z
ones(3)               #   x+y+z
constant(3)           #   1 + 0x + 0y + 0z
zero(3)               #   0 + 0x + 0y + 0z
homog(3,2)            #   x^2 + y^2 + z^2 + xy + xz + yz

# now some multivariate factorization:

ones(2)*linear(c(1,-1))                                       # x^2-y^2
ones(2)*(linear(c(1,1),2)-uni(2))                             # x^3+y^3
linear(c(1,-1))*homog(2,2)                                    # x^3+y^3 again
ones(2)*(ones(2,4)+uni(2)^2-product(c(1,3))-product(c(3,1)))  # x^5+y^5
ones(2)*homog(2,4,c(1,-1,1,-1,1))                             # x^5+y^5 again

Partial differentitation

Description

Partial differentiation with respect to any variable

Usage

## S3 method for class 'multipol'
deriv(expr, i, derivative = 1, ...)

Arguments

expr

A multipol

i

Dimension to differentiate with respect to

derivative

How many times to differentiate

...

Further arguments, currently ignored

Author(s)

Robin K. S. Hankin

Examples

a <- as.multipol(matrix(1:12,3,4))

deriv(a,1)     # standard usage: derivfferentiate WRT x1
deriv(a,2)     # differentiate WRT x2

deriv(a,1,2)   # second derivative
deriv(a,1,3)   # third derivative (zero multipol)

Is a multivariate polynomial constant or zero?

Description

Is a multivariate polynomial constant or zero?

Usage

is.constant(a, allow.untrimmed = TRUE)
is.zero(a, allow.untrimmed = TRUE)

Arguments

a

A multipol

allow.untrimmed

Boolean with default TRUE meaning to allow a multipol to be zero/constant even if one or more array extents exceed 2

Author(s)

Robin K. S. Hankin

Examples

is.zero(linear(c(1,1i))*linear(c(1,-1i)) - ones(2,2))  # factorize x^2+y^2

Coerce and test for multipols

Description

Coerce and test for multipols

Usage

multipol(x)
as.multipol(x)
is.multipol(x)

Arguments

x

Object to be coerced to multipol

Details

The usual case is to coerce an array to a multipol. A character string may be given to as.multipol(), which will attempt to coerce to a multipol.

Note

Subsets of a multipol are accessed and set using Oarray-style extraction with an offset of zero.

Author(s)

Robin K. S. Hankin

Examples

a <- as.multipol(array(1:12,c(2,3,2)))

One over one minus a multipol

Description

Uses Taylor's theorem to give one over one minus a multipol

Usage

ooom(n, a, maxorder=NULL)

Arguments

n

The order of the approximation; see details

a

A multipol

maxorder

A vector of integers giving the maximum order as per taylor()

Details

The motivation for this function is the formal power series (1-x)^{-1}=1+x+x^2+\ldots. The way to think about it is to observe that (1+x+x^2+\ldots+x^n)(1-x)=1-x^{n-1}, even if x is a multivariate polynomial (one needs only power associativity and a distributivity law, so this works for polynomials). The right hand side is 1 if we neglect powers of x greater than the n-th, so the two terms on the left hand side are multiplicative inverses of one another.

Argument n specifies how many terms of the series to take.

The function uses an efficient array method when x has only a single non-zero entry. In other cases, a variant of Horner's method is used.

Author(s)

Robin K. S. Hankin

References

I. J. Good 1976. “On the application of symmetric Dirichlet distributions and their mixtures to contingency tables”. The Annals of Statistics, volume 4, number 6, pp1159-1189; equation 5.6, p1166

Examples

ooom(4,homog(3,1))


# How many 2x2 contingency tables of nonnegative integers with rowsums =
# c(2,2) and colsums = c(2,2) are there?  Good gives:

(
  ooom(2,lone(4,c(1,3))) *
  ooom(2,lone(4,c(1,4))) *
  ooom(2,lone(4,c(2,3))) *
  ooom(2,lone(4,c(2,4))) 
)[2,2,2,2]
  
# easier to use the aylmer package:

## Not run: 
library(aylmer)
no.of.boards(matrix(1,2,2))

## End(Not run)

Multivariate polynomial product

Description

Gives an generalized outer product of two multipols

Usage

polyprod(m1, m2, overlap = 0)

Arguments

m1, m2

multipols to be combined

overlap

Integer indicating how many variables are common to m1 and m2; default of zero corresponds to no variables in common

Author(s)

Robin K. S. Hankin

Examples

a <- as.multipol(matrix(1,2,2))     # 1+x+y+xy

polyprod(a,a)       # (1+x+y+xy)*(1+z+t+zt)   --- offset=0
polyprod(a,a,1)     # (1+x+y+xy)*(1+y+z+yz)
polyprod(a,a,2)     # (1+x+y+xy)^2

Print method for multipols

Description

Print methods for multipols

Usage

## S3 method for class 'multipol'
print(x, ...)
do_dimnames(a, include.square.brackets = getOption("isb"), varname =
getOption("varname"), xyz = getOption("xyz"))
## S3 method for class 'multipol'
as.character(x, ..., xyz = getOption("xyz"), varname =
getOption("varname"))

Arguments

a, x

Multipol or array

include.square.brackets

Boolean with TRUE meaning to, er, include square brackets in the dimnames (eg [x3]^5) and default FALSE meaning to omit them (eg x3^5)

varname

String to describe root variable name (eg varname="y" gives y3^5 or [y3]^5)

xyz

Boolean with default TRUE meaning to represent multipols of dimension d\leq 3 using x, y, and z for the variable names and FALSE meaning to use x1, x2, x3. This option is ignored if d>3; see examples section

...

Further arguments (currently ignored)

Details

Function do_dimnames() is a helper function that takes an array and gives it dimnames appropriate for expression as a multipol. Default behaviour is governed by options isb, varname, and xyz. The function might be useful but it is really intended to be called by print.multipol().

The default behaviour of do_dimnames() and as.character(), and hence the print method for multipols, may be modified by using the options() function. See examples section below.

Author(s)

Robin K. S. Hankin

Examples


ones(2,5)

options("showchars" = TRUE)
ones(2,5)

options("xyz" = FALSE)
ones(2,5)

options("varname" = "fig")
ones(2,5)

options("showchars" = FALSE)
ones(2,5)

do_dimnames(matrix(0,2,3),varname="fig",include=TRUE)

Substitute a value for a variable

Description

Substitute a value for a variable and return a multipol of arity d-1

Usage

put(a, i, value, keep = TRUE)

Arguments

a

multipol

i

Dimension to substitute

value

value to substitute for x[i]

keep

Boolean with default TRUE meaning to retain singleton dimensions and FALSE meaning to drop them

Author(s)

Robin K. S. Hankin

Examples


a <- as.multipol(matrix(1:12,3,4))
put(a,1,pi)
put(a,2,pi)

b <- as.multipol(array(1:12,c(3,2,3)))

put(b,2,pi,TRUE)
put(b,2,pi,FALSE)

Remove redundant entries from a multipol

Description

Remove redundant entries from a multivariate polynomial: function trim() trims the array of non-significant zeroes as far as possible without altering its value as a multipol; function taylor() returns the multivariate Taylor expansion to a specified order.

Usage

trim(a)
taylor(a,maxorder=NULL)

Arguments

a

A multipol

maxorder

The multivariate order of the expansion returned; default of NULL means to return a unaltered

Value

Returns a multipol

Note

If a is a zero multipol (that is, a multivariate polynomial with all entries zero) of any size, then trim(a) is a zero multipol of the same arity as a but with extent 1 in each direction.

Author(s)

Robin K. S. Hankin

Examples

a <- matrix(0,7,7)
a[1:3,1:4] <- 1:12
a <- as.multipol(a)
a
trim(a)
taylor(a,2)

Multivariate polynomials

Description

Details

Author(s)

Examples

Extract or Replace Parts of a multipol

Description

Usage

Arguments

Details

Author(s)

References

Examples

Arithmetic ops group methods for multipols

Description

Usage

Arguments

Details

Author(s)

See Also

Examples

Coerce multipols to arrays

Description

Usage

Arguments

Author(s)

Examples

Coerce a multipol to a function

Description

Usage

Arguments

Author(s)

See Also

Examples

Various useful multivariate polynomials

Description

Usage

Arguments

Details

Note

Author(s)

See Also

Examples

Partial differentitation

Description

Usage

Arguments

Author(s)

See Also

Examples

Is a multivariate polynomial constant or zero?

Description

Usage

Arguments

Author(s)

See Also

Examples

Coerce and test for multipols

Description

Usage

Arguments

Details

Note

Author(s)

See Also

Examples

One over one minus a multipol

Description

Usage

Arguments

Details

Author(s)

References

See Also

Examples

Multivariate polynomial product

Description

Usage

Arguments

Author(s)