Calculate the residual (slack) between the input and the bounds

For a bound constraint of the form:

lb <= x <= ub

the lower and upper residuals between x and the bounds are values sl and sb such that:

lb + sl == x == ub - sb

When all elements of sl and sb are positive, all elements of x lie within the bounds; a negative element in sl or sb indicates that the corresponding element of x is out of bounds.

x: array_like

Vector of independent variables

sl, sbarray-like

The lower and upper residuals