Logic:

+ logical values:
  0 (false) and 1 (true) (actually, anything non-zero is true)
+ logical operators:
  & (and), | (or), ~ (not), xor (exclusive or)
+ relational operators:
  >, >=, <, <=, ==, ~=
+ examples) 
  1 < 2            % less than
  1 == 1           % equal (true)
  1 == 2           % equal (false)
  1==1   &   2==2  % true
  1 > 2  |  1 < 2  % true
  xor(1 < 2,1 < 3) % false
  5 & 10           % true (anything non-zero is technically true!)
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Logical Arrays
+ an array of logical values
+ operations are applied to each element one at a time
+ MATLAB stores 1 or 0 depending on the truth of the relation for each element

  >> x = [1 2 3];
  >> y = x >= 2

+ to extract elements that correspond to TRUE relations, use
  array(logicalarray)

  >> x(y)

+ Example 2: find even integers from an array
  >> z = 0:10;         % array from 0 to 10
  >> k = mod(z,2)==0;  % $k$ is a logical array
  >> z(k)              % extract even integers from $k$

+ WARNING:
  to generate logical array, MUST use relations, not just enter 0 and 1!

  >> z=3:5;     % array of ints from 3 to 5
  >> q=[0 1 0]; % array of what appears to be logical values (but isn't!)
  >> z(q)       % attempt to extract elements from $z$ (but won't work)
  output is the error mesg: 
    ??? Index into matrix is negative or zero. See release notes on changes to 
    logical indices.
  >> To fix, use $logical$ function:
  >> z(logical(q))

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