The purpose of this lab is to acquaint you with techniques for finding global extreme values of functions of two variables.
cp /math/calclab/MA1024/Optimization_start.mws My_Documents
You can copy the worksheet now, but you should read through the lab before you load it into Maple. Once you have read to the exercises, start up Maple, load the worksheet Optimization_start.mws, and go through it carefully. Then you can start working on the exercises.
A crucial first step in solving such problems is being able to find
and classify local extreme values of a function. What we mean by a
function having a local extreme value at a point
is
that for values of
near
,
for a local maximum and
for a local minimum.
In single-variable
calculus, we found that we could locate candidates for local extreme
values by finding points where the first derivative vanishes. For
functions of two dimensions, the condition is that both first order
partial derivatives must vanish at a local extreme value candidate
point. Such a point is called a stationary point. It is also one of
the three types of points called critical points.
Note carefully that the condition does not say that a point where the partial
derivatives vanish must be a local extreme point. Rather, it says that
stationary points are candidates for local extrema. Just as was the case
for functions of a single variable, there can be stationary points that
are not extrema. For example, the saddle surface
has a stationary point at the origin, but it is not a local extremum.
Finding and classifying the local extreme values of a function
requires several steps. First, the partial derivatives must
be computed. Then the stationary points must be solved for by finding where both first partial derivatives are zero simultaneously, which is not
always a simple task. Next, one must check for the presence of
singular points, which might also be local extreme
values. Finally, each
critical point must be classified
as a local maximum, local minimum, or neither. The examples in the
Getting Started worksheet
are intended to help you learn how to use Maple to simplify these tasks.
The basic theorem on the existence of global maximum and minimum values is the following.