Some of you are trying scilab, here are a couple of tricks to make
your life easier.

The scilab commands I used Friday are in the file 07sep07.sci in our
local scilab directory.
	http://www.math.fsu.edu/~bellenot/class/f07/em2/scilab/

Here are some scilab hints.

HINT 0
When want to erase the plot (because some error) you can use the
command clf() or the file-menu-item clear 

HINT 1
For reasons that make no sense to me the obvious
collection of commands fails to define the function h(x) correctly

function y = h(x)
if abs(x) < %pi/2 then y = 1; else y = -1; end
endfunction

Well h(0) and h(2) will work but h(t) where t=-%pi:0.05:%pi will fail.

Instead use the following function definition (type one line at time)
This makes y an array of -1's the same size as x and then changes
those entries y(i) to 1 when x(i) is between -pi/2 and pi/2.

function y = h(x)                               
y=-1*ones(x); // this defines a matrix of -1's
y(find( x<%pi/2 & x>-%pi/2 )) = 1; // when |x|<pi/2, value now 1
endfunction

CAUTION this h(x) is only defined correctly for x's in the range
-pi to pi (well by luck it is actually correct from -3pi/2 to 3pi/2)

HINT 2
The for loop needed to obtain the 21st approximation can be done
trig21 = zeros(t)
for i=1:21, trig21 = trig21 + (4/%pi)*sin(i*%pi/2)*cos(i*t)/i; end;

HINT 3
To make a postscript file of graphic window 0, one can use the 
file-menu-item export or the command xs2eps(0,"foo.eps")