%
%  my first matlab script
%     (note the "percent" signs indicate non-executed comment lines)
%
%  save as: "wilk.m"
%
%  to run:  type "wilk" at the matlab prompt (note:  you may have to set 
%     the directory/folder into the matlab path), or use the "run" menu
%     choice (not sure of exact PC name of run script menu choice).
%
%  browser help:  type "helpdesk" at the matlab prompt
%
%  instant help:  type "help xxxx" for help about command xxxx
%     (try "help clf", etc)
%
%- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 

%  define some parameters

N = 7;  a = 0.00002;

%  define a vector of x-values

x = 0:0.025:N+1;

%  loop to evaluate y1(x) = (x-1)(x-2)...(x-N)

y1 = ones(size(x));

for j=1:N
  y1 = y1.*(x-j);
end

%  evaluate y2(x)
%  (note "." denote element-wise operation:  "help arith")

y2 = a*N*(N+1)/2*x.^(N-1);

%  make a LABELLED plot

clf
plot(x,y1,'b');  hold on;
plot([0 N+1],[0 0],'k')
plot(x,y2,'r--')

axis([0 N+1 -100 200])

title('\bf wilkinson''s example')
xlabel('\bf x-axis (in boldface)')
ylabel('y-axis (not in \bf boldface\rm)')
text(3,100,'roots are where blue & red curves cross')

disp('check out:  exercise 2, page 23 of holmes')