"Non-" should always be hyphenated, unless it is simply joined to the word (eg. nonlinear). "Non-" should always be hyphenated, unless it is simply joined to theword (eg. nonlinear).

Which is correct nonlinear or non linear?

However, this doesn't excuse "non-linear" as the term is common in mathematics (which I hope we all took to a point where this term is known); the spelling is "nonlinear" and the hyphen should not be used here.

Should I put a hyphen after non?

The prefix non- may be joined to a word by means of a hyphen, which is standard in British usage. In many cases, especially in American usage, non- is joined without a hyphen. ... Some non- words rarely or never use a hyphen (such as nonentity). By contrast, un- is almost always spelled without a hyphen.