logical1.m

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%  Script file: logical1.m
%
%  Purpose: 
%    This program calculates the time required to 
%    calculate the square roots of all elements in
%    array a whose value exceeds 5000.  This is done 
%    in two different ways:
%    1.  Using a for loop and if construct.
%    2.  Using a logical array.
%
%  Record of revisions:
%      Date       Programmer          Description of change
%      ====       ==========          =====================
%    01/27/07    S. J. Chapman        Original code 
%
% Define variables:
%   a            -- Array of input values
%   b            -- Logical array to serve as a mask
%   ii, jj       -- Loop index
%   average1     -- Average time for calculation 1
%   average2     -- Average time for calculation 2
%   maxcount     -- Number of times to loop calculation
%   month        -- Month (mm)
%   year         -- Year (yyyy)


% Perform calculation using loops and branches.
maxcount = 10;              % Number of repetitions
tic;                        % Start timer
for jj = 1:maxcount        
   a = 1:10000;             % Declare array a
   for ii = 1:10000    
      if a(ii) > 5000
         a(ii) = sqrt(a(ii));
      end
   end
end
average1 = (toc)/maxcount;  % Calculate average time 


% Perform calculation using logical arrays.
maxcount = 100;             % Number of repetitions
tic;                        % Start timer
for jj = 1:maxcount        
   a = 1:10000;             % Declare array a
   b = a > 5000;            % Create mask
   a(b) = sqrt(a(b));       % Take square root
end
average2 = (toc)/maxcount;  % Calculate average time 

% Display results
fprintf('Loop / if approach =     %8.4f\n', average1);
fprintf('Logical array approach = %8.4f\n', average2);