# Terminology: generic word for increase and decrease

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.

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Can't you just say "x may be negative" in a comment? – Qiaochu Yuan Feb 4 '11 at 21:12
I have but it would be better for it to be part of the method name, which is currently increaseLengthBy: – Jonathan. Feb 4 '11 at 21:18
@Jonathan: Well, if want to allow x to be either positive or negative (or 0), why not say "The length of a painted line changes by x"? Then the method could be changeLengthBy. The generic term is "change". – Arturo Magidin Feb 4 '11 at 21:37
Or, "adjusted" so that the method could be adjustLenthBy. One of the guidelines in Microsoft's opus Code Complete is to use strong verbs in function names. Actually I like the use of negative arguments with increaseLengthBy. I should think it would make perfect sense to any mathematician who programs. – hardmath Feb 5 '11 at 2:58
@hardmath, could you put that as an answer? – Jonathan. Feb 9 '11 at 18:43

As a "neutral" verb regarding increase or decrease, I propose "adjust" so that the method would be adjustLengthBy. This is concise but conforms to the MS Code Complete dictum to use strong verbs in function names.
I'd say that "A painted line is changed by length $x$." The use of 'increased' implies the change is positive and it sends a confusing mixed message.