This is a really basic question. Consider a statement:
A painted line is increased by length $x$
Can $x$ be a negative number just by the wording of the question? What would be a better way of rephrasing the question, to make it clear that $x$ can be negative?
(The reason I'm asking is that I'm programming and a method name needs to indicate that the parameter can be negative or positive, in order to decrease or increase a size)
Basically I'm looking for a generic term for decrease and increase.