For spikey.

http://www.twoplustwo.com/cgi-bin/newforums/genpok.pl?read=34365

The second derivative can be zero if you have a maximum or a minimum.


In the case of a maximum, the second derivative is still negative on both sides surrounding the maximum.


I don't remember seeing this when I went to school (a long time ago now), thank you for pointing this out to me.


I've been studying partial derivatives lately, I don't remember learning those either, but they seem so useful now.


Regards