I am a big fan of Ternary Search.

But the fact that we can use it only in strictly increasing and strictly decreasing functions upsets me.

I am asking how to deal with functions which can have equal values (i.e. $$$f(i) <= f(i + 1)$$$ $$$[i < j]$$$, $$$f(i) >= f(i + 1)$$$ $$$[i >= j]$$$).

For example with this function $$$f(x) =$$$ {$$$1, 2, 1, 1, 1, 1, 1, 1, 1, 1$$$}.