提高m文件的运行速度(2)

橄榄之家

m文件的不同编程风格对程序的运行速度也有比较大的影响，下面的代码比较了采用for 循环关系运算赋值，for循环＋if 语句以及直接采用数组运算的运行速度。比较的结果第三种方法采用数组直接运算最快，第一种方法次之，第二种方法最慢。第一种方法的运行速度约为第三种方法的两到三倍，第二种方法为第三种方法的三到四倍。

具体在我的电脑中的一次运行结果为：0.28125秒，0.39063和0.09375。

function PerformanceComp()
Length = 10^7;
Source = round(rand(Length, 1)) * 2 - 1;

%% to evaluate the for loop time with memory allocation first
StartTime = cputime;
Res = zeros(Length, 1);
for i=1ength
??? Res(i) = Source(i) >= 0;
end
EndTime = cputime;
Duration = EndTime - StartTime;
disp(['The for loop with memory allocation running time is ' num2str(Duration)]);
%% to evaluate the for loop time with memory allocation first
%? with if else clause
StartTime = cputime;
Res = zeros(Length, 1);
for i=1ength
??? if Source(i) >= 0
??????? Res(i) = 1;
??? else
??????? Res(i) = 0;
??? end
end
EndTime = cputime;
Duration = EndTime - StartTime;
disp(['The for loop with memory allocation running time' ...
??? 'with if clause is ' num2str(Duration)]);
%% to evaluate the array operation running time
StartTime = cputime;
Res = Source >= 0;
EndTime = cputime;
Duration = EndTime - StartTime;
disp(['The array operation time is ' num2str(Duration)]);