Increment and decrement operators — increment • hyper2

Syntactic sugar for incrementing and decrementing likelihood functions.

Frankly they don't do anything that magrittr:add() and magrittr:subtract() don't (except have a default value of 1 (which is surprisingly useful).

inc(H, val = 1)
dec(H, val = 1)
trial(winners,players,val=1)

Arguments

H: A hyper2 object
winners, players: Numeric or character vectors specifying the winning team and the losing team
val: Numeric

Details

A very frequent operation is to increment a single term in a hyper2 object. If


> H <- hyper2(list("a",c("a","b"),"c",c("a","b","c")),c(1:3,-6))
> H
log( a * (a + b + c)^-6 * b^2 * c^3)

Suppose we wish to increment the power of a+b. We could do:


H[c("a","b")] <- H[c("a","b")] + 1

(see the discussion of hyper2_sum_numeric at Ops.hyper2.Rd; also vignette zeropower). Alternatively we could use magrittr pipes:


H[c("a","b")] %<>% add(1)

But inc and dec furnish convenient idiom to accomplish the same thing:


H[c("a","b")] %<>% inc

Functions inc and dec default to adding or subtracting 1, but other values can be supplied:


H[c("a","b")] %<>% inc(3)

Or even


H[c("a","b")] %<>% inc(H["a"])

The convenience function trial() takes this one step further and increments the ‘winning team’ and decrements the bracket containing all players. The winners are expected to be players.


> trial(c("a","b"),c("a","b","c"))
> (a + b) * (a + b + c)^-1

Using trial() in this way ensures that the powers sum to zero.


  H <- trial(c("a","b"),c("a","b","c"))
  H %<>% inc(trial("a",c("a","b")))
  H

The inc and dec operators and the trial() function are used in inst/kka.Rmd.

Author

Robin K. S. Hankin

Examples

data(chess)

## Now suppose we observe an additional match, in which Topalov beats
## Anand.  To incorporate this observation into the LF:



trial("a",c("a","b"))
#> log( a * (a + b)^-1)

chess <- chess + trial("Topalov",c("Topalov","Anand"))