www.pudn.com > matlab±à³Ì.zip > timings.m, change:1997-12-30,size:2571b

%  Script file: timings.m 
% 
%  Purpose:  
%    This program calculates the time required to  
%    calculate the squares of all integers from 1 to 
%    10,000 in three different ways: 
%    1.  Using a for loop with an uninitialized output 
%        array. 
%    2.  Using a for loop with an pre-allocated output 
%        array. 
%    3.  Using vectors. 
% 
%  Record of revisions: 
%      Date       Programmer          Description of change 
%      ====       ==========          ===================== 
%    12/08/97    S. J. Chapman        Original code  
% 
% Define variables: 
%   ii, jj       -- Loop index 
%   average1     -- Average time for calculation 1 
%   average2     -- Average time for calculation 2 
%   average3     -- Average time for calculation 3 
%   maxcount     -- Number of times to loop calculation 
%   square       -- Array of squares 
%   leap_day     -- Extra day for leap year 
%   month        -- Month (mm) 
%   year         -- Year (yyyy) 
 
 
% Perform calculation with an uninitialized array  
% "square".  This calculation is done only once  
% because it is so slow. 
maxcount = 1;               % One repetition 
tic;                        % Start timer 
for jj = 1:maxcount         
   clear square             % Clear output array 
   for ii = 1:10000        
     square(ii) = ii^2;     % Calculate square 
   end 
end 
average1 = (toc)/maxcount;  % Calculate average time  
 
 
% Perform calculation with a pre-allocated array  
% "square".  This calculation is averaged over 10   
% loops. 
maxcount = 10;              % One repetition 
tic;                        % Start timer 
for jj = 1:maxcount         
   clear square             % Clear output array 
   square = zeros(1,10000); % Pre-initialize array 
   for ii = 1:10000        
     square(ii) = ii^2;     % Calculate square 
   end 
end 
average2 = (toc)/maxcount;  % Calculate average time  
 
% Perform calculation with vectors.  This calculation  
% averaged over 100 executions.  
maxcount = 100;             % One repetition 
tic;                        % Start timer 
for jj = 1:maxcount         
   clear square             % Clear output array 
   ii = 1:10000;            % Set up vector 
   square = ii.^2;          % Calculate square 
end 
average3 = (toc)/maxcount;  % Calculate average time  
 
% Display results 
fprintf('Loop / uninitialized array = %8.4f\n', ... 
         average1); 
fprintf('Loop / initialized array =   %8.4f\n', ... 
         average2); 
fprintf('Vectorized =                 %8.4f\n', ... 
         average3);