QCA (version 3.3)

negate: Negate Boolean expressions

Description

Function to negate a SOP expression.

Usage

negate(expression, snames = "", noflevels, use.tilde = FALSE)

Arguments

expression

A string representing a SOP expression, or a minimization object of class "qca".

snames

A string containing the sets' names, separated by commas.

noflevels

Numerical vector containing the number of levels for each set.

use.tilde

Logical, use tilde for negation with bivalent variables.

Value

A list with the following two components:

initial	The initial expression.
negated	The negation of the initial expression.

If expression is an object of type "qca", the result is a list of solutions.

Details

In Boolean algebra, there are two transformation rules named after the British mathematician Augustus De Morgan. These rules state that:

1. The complement of the union of two sets is the intersection of their complements.

2. The complement of the intersection of two sets is the union of their complements.

In "normal" language, these would be written as:

1. not (A and B) = (not A) or (not B)

2. not (A or B) = (not A) and (not B)

Based on these two laws, any Boolean expression written in disjunctive normal form can be transformed into its negation.

It is also possible to negate all models and solutions from the result of a Boolean minimization from function minimize(). The resulting object, of class "qca", is automatically recognised by this function.

In a SOP expression, the products should normally be split by using a star * sign, otherwise the sets' names will be considered the individual letters in alphabetical order, unless they are specified via snames.

To negate multilevel expressions, the argument noflevels is required.

References

Ragin, Charles C. 1987. The Comparative Method: Moving beyond Qualitative and Quantitative Strategies. Berkeley: University of California Press.

See Also

minimize

Examples

# NOT RUN {
# example from Ragin (1987, p.99)
negate("AC + B~C")

# with different intersection operators
negate("AB*EF + ~CD*EF")


# using an object of class "qca" produced with minimize()
data(LC)
cLC <- minimize(LC, outcome = "SURV")

negate(cLC)


# parsimonious solution
pLC <- minimize(LC, outcome = "SURV", include = "?")

negate(pLC)

# }