# flipsign

flipsign(x, y)

Return `x` with its sign flipped if `y` is negative. For example `abs(x) = flipsign(x,x)`.

## Examples

``````julia> flipsign(2, -1)
-2``````
``````julia> flipsign(2, abs(-1))
2``````
1. Flip the sign of a positive number when `y` is negative:

``````julia> flipsign(10, -5)
-10``````

In this example, since `y` is negative, the sign of `x` (which is 10) is flipped to -10.

2. No sign flip when `y` is positive:

``````julia> flipsign(8, 3)
8``````

Here, `y` is positive, so the sign of `x` (which is 8) remains unchanged.

3. Flip the sign of a negative number when `y` is negative:

``````julia> flipsign(-15, -2)
15``````

In this case, both `x` and `y` are negative, so the sign of `x` (which is -15) is flipped to positive 15.

4. Using `flipsign` with the `abs` function:
``````julia> abs_val = flipsign(7, 7)
7``````

This example demonstrates the relationship between `flipsign` and the `abs` function. Since `y` is positive, `flipsign` returns `x` as is, and therefore, `abs(x) = flipsign(x,x)`.

Common mistake example:

``````julia> flipsign(3, 0)
ERROR: DomainError with -0.0:``````

In this example, the function call results in a `DomainError` because `y` is zero. The `y` argument must be a non-zero number to avoid this error. Make sure to provide a valid and non-zero `y` value when using `flipsign`.