# Monotonic

(Redirected from Monotone)
This page is a stub, so it contains little or minimal information and is on a to-do list for being expanded.The message provided is:
I made this just to make it blue
This page requires references, it is on a to-do list for being expanded with them.
Please note that this does not mean the content is unreliable, it just means that the author of the page doesn't have a book to hand, or remember the book to find it, which would have been a suitable reference.
The message provided is:
Find an order theory book, also I think that huge category theory PDF (Harold Simmons) has it

## Definition

A map, [ilmath]f:X\rightarrow Y[/ilmath] between two posets, [ilmath](X,\sqsubseteq)[/ilmath] and [ilmath](Y,\preceq)[/ilmath] is monotonic or monotone if:

• [ilmath]\forall a,b\in X[a\sqsubseteq b\implies f(a)\preceq f(b)][/ilmath], or in words:
• It preserves the ordering.

### For a sequence

Recall that a sequence, [ilmath] ({ A_n })_{ n = 1 }^{ \infty }\subseteq X [/ilmath] (for some poset, [ilmath](X,\sqsubseteq)[/ilmath]) can be considered as a mapping:

• [ilmath]A:\mathbb{N}\rightarrow X[/ilmath] given by [ilmath]A:n\mapsto A_n[/ilmath]

We can now apply the above definition directly.

## Work needed

TODO: These

1. How can we have monotonically decreasing things? Via the dual partial ordering of course! To have [ilmath]\le[/ilmath] is to induce a unique [ilmath]\ge[/ilmath] - these are distinct orderings.
2. Not sure, but probably some call this isotonic, while monotonic is either increasing or decreasing.
3. Unite with monotonic set function