D.5.4 Additional gsldif notes

The function f may be any expressible virtual machine code function that takes a real argument to a real result, including one that uses other library functions. However, if f passes functions to other library functions as arguments, there is a constant overhead in stack space for each level, and a remote possibility of a segmentation fault if they are very deeply nested.

Numerical instability is an issue for higher derivatives (i.e., differentiating a function that is obtained by differentiating another function). Some experimentation with larger tolerances may be needed.