subs {freealg}

Substitution

Description

Substitute symbols in a freealg object for numbers or other freealg objects

Usage

subs(S, ...)
subsu(S1,S2,r)

Arguments

S, S1, S2

Objects of class freealg

r

Integer specifying symbol to substitute (a=1,b=2 etc)

...

named arguments corresponding to variables to substitute

Details

Function subs() substitutes variables for freealg objects (coerced if necessary) using natural R idiom. Observe that this type of substitution is sensitive to order:

> subs("ax",a="1+x",x="1+a")
free algebra element algebraically equal to
 + 2 + 3*a + 1*aa

> subs("ax",x="1+a",a="1+x")
free algebra element algebraically equal to
 + 2 + 3*x + 1*xx

Functions subsu() is a lower-level formal function, not really intended for the end-user. Function subsu() takes S1 and substitutes occurrences of symbol r with S2.

No equivalent to mvp::subvec() is currently implemented.

Value

Returns a freealg object.

Note

Function subs() is one place in the package where the use of letters is effectively hard-wired in. Idiom such as

subs("abccc",b="1+3x")

is very nice, but identifies “b” with 2. Note that argument r of subsu() is canonically an integer but a single character is interpreted as a letter. See also the note at freealg.Rd.

Author(s)

Robin K. S. Hankin

Examples

subs("abccc",b="1+3x")
subs("aaaa",a="1+x")  # binomial

subs("abA",b=31)

subs("1+a",a="A")   # can substitute for an inverse
subs("A",a="1+x")   # inverses are not substituted for


## Sequential substitution works:

subs("abccc",b="1+3x",x="1+d+2e")
subs(rfalg(),a=rfalg())