Writing fast Matlab codes

uqHZau · 发表于 2020-8-4 14:14

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1. 使用profile

profile on, profile clear
example(5000);  %此处可为任何你要运行的代码
profile report

2. Array Preallocation

代码1：
tic;
a(1) =1;
b(1) = 0;
for k=2:10000
  a(k) = 0.99803 * a(k-1) - 0.06279*b(k-1);
  b(k) = 0.06279 * a(k-1) + 0.99803*b(k-1);
end
toc;

结果为:
Elapsed time is 0.475989 seconds.
而且代码中a，b下面会有红色的波浪线提示，

修改后的代码2：
tic;
a= zeros(1,10000);
b = zeros(1,10000);
a(1) =1;
b(1) = 0;
for k=2:10000
a(k) = 0.99803 * a(k-1) - 0.06279*b(k-1);
b(k) = 0.06279 * a(k-1) + 0.99803*b(k-1);
end
toc;

结果为：
Elapsed time is 0.000581 seconds.

3. JIT Acceleration

4. Vectorization
Consider following function:
function d= minDistance(x,y,z)
nPoints = length(x);
d=zeros(nPoints,1);
for k=1:nPoints
d(k) = sqrt(x(k)^2+ y(k)^2+z(k)^2);
end
d=min(d);
end

function d= minDistance2(x,y,z)
d= sqrt(min(x.^2+y.^2+z.^2));
end

测试：
clear all;
clc;
nPoints = 100000;
x = rand(nPoints,1);
y = rand(nPoints,1);
z = rand(nPoints,1);

tic;
d=minDistance(x,y,z);
toc;

tic;
d=minDistance2(x,y,z);
toc;

结果如下：
Elapsed time is 0.010904 seconds.
Elapsed time is 0.003773 seconds.

CCxiaom · 发表于 2020-8-4 14:37

Writing fast Matlab codes

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Writing fast Matlab codes

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