%---------------------------------------------------------
%
% For A321 course
%
%-------------------------------------------------------------
%
%    Randall Bramley
%    Department of Computer Science
%    Indiana University, Bloomington
%    bramley somewhere at cs dot indiana dot (allegedly) edu                             
%
% Started: Mon 04 Feb 2008, 09:05 AM
% Last Modified: Mon 16 Feb 2009, 03:42 PM
%
%-------------------------------------------------------------

more on
echo on
%---------------------------------------------------------
% Logical operators return 0 (false) or 1 (true). This
% is a bad programming practice but started with C coding
% back in the 1970's and now it is deeply embedded in much
% of numerical computing.
%---------------------------------------------------------


%-------------------------------------------
% First, set up a simple vector to work with
%-------------------------------------------
a = 1:9

% greater than is >
t1 = a >  4
% less than is <
t2 = a <  4
% greater than or equal to is >= 
t3 = a >= 4
% less than or equal to is  <=
t4 = a <= 4

%--------------------------------------------------------------
% Notice that the last two have the inequality operator (<, >)
% appearing *before* the equality operator (=).
%--------------------------------------------------------------

%-----------------------------------------------------------------
% The next is a test for where a is equal to 4, not to be confused
% with the assignment statement
%      a = 4
% which would reset the 1x9 vector a to be the  1x1 scalar value 4
%-----------------------------------------------------------------
t5 = a == 4


t6 = a ~= 4

%---------------------------------------------------------------
% The inequality operator ~= can take the forms
%       !=
%       /=
%       ^=
%      .ne. 
% in other languages, so it's one to check on in each case.
% The others are standard in C, C++, Fortran, Perl, Python, ....
%
% The find() function is not the same; it returns a set of
% indices, not just true or false (or 1 and 0).
%---------------------------------------------------------------
I = find(a >= 4)

echo off;
more off;