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Constraint sets, for building a program by hand

Source: R/ir.R
consets.Rd

In a program(), a constraint states that an expression lies in a set:

Usage

zero()

nonneg()

indicator(bin, inner)

Arguments

bin

The binary variable that switches the constraint on, as an ir_var() node.

inner

The set the expression must lie in when bin is 1: zero() or nonneg().

Value

A plain list without a class, to be passed as the set of a constraint(): list(kind = "zero"), list(kind = "nonneg"), or for indicator() a list with kind = "indicator" and the fields bin and inner.

Details

  • zero(): the expression equals 0;

  • nonneg(): the expression is at least 0;

  • indicator(bin, inner): the expression lies in the set inner whenever the binary variable bin is 1, and is unrestricted when it is 0.

So x + 2 * y <= 5 is written as 5 - (x + 2 * y) in nonneg(), and x == 3 as x - 3 in zero(). add() makes this conversion for you.

Examples

# x + 2 * y <= 5
constraint(ir_apply("-", list(ir_const(5),
                              ir_apply("+", list(ir_var("x"),
                                                 ir_apply("*", list(ir_const(2), ir_var("y"))))))),
           nonneg())
#> $f
#> $f$kind
#> [1] "apply"
#> 
#> $f$op
#> [1] "-"
#> 
#> $f$args
#> $f$args[[1]]
#> $f$args[[1]]$kind
#> [1] "const"
#> 
#> $f$args[[1]]$value
#> [1] 5
#> 
#> 
#> $f$args[[2]]
#> $f$args[[2]]$kind
#> [1] "apply"
#> 
#> $f$args[[2]]$op
#> [1] "+"
#> 
#> $f$args[[2]]$args
#> $f$args[[2]]$args[[1]]
#> $f$args[[2]]$args[[1]]$kind
#> [1] "var"
#> 
#> $f$args[[2]]$args[[1]]$name
#> [1] "x"
#> 
#> $f$args[[2]]$args[[1]]$index
#> list()
#> 
#> 
#> $f$args[[2]]$args[[2]]
#> $f$args[[2]]$args[[2]]$kind
#> [1] "apply"
#> 
#> $f$args[[2]]$args[[2]]$op
#> [1] "*"
#> 
#> $f$args[[2]]$args[[2]]$args
#> $f$args[[2]]$args[[2]]$args[[1]]
#> $f$args[[2]]$args[[2]]$args[[1]]$kind
#> [1] "const"
#> 
#> $f$args[[2]]$args[[2]]$args[[1]]$value
#> [1] 2
#> 
#> 
#> $f$args[[2]]$args[[2]]$args[[2]]
#> $f$args[[2]]$args[[2]]$args[[2]]$kind
#> [1] "var"
#> 
#> $f$args[[2]]$args[[2]]$args[[2]]$name
#> [1] "y"
#> 
#> $f$args[[2]]$args[[2]]$args[[2]]$index
#> list()
#> 
#> 
#> 
#> 
#> 
#> 
#> 
#> 
#> $set
#> $set$kind
#> [1] "nonneg"
#> 
#> 
#> $over
#> list()
#>