matlab基础2

Dear 丶 2022-02-23 05:28 248阅读 0赞

# 1. matlab网上资源 #

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbnlhbndlbm1lbmc_size_16_color_FFFFFF_t_70][]

# 2. 向量化编程 #

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbnlhbndlbm1lbmc_size_16_color_FFFFFF_t_70 1][]

a = rand(10000);
    b = rand(10000);
    clear a
    b = rand(10000);

不需要a就及时把它清理掉。

1. 及时清除不用的变量

a = rand(10000);
    b = rand(10000);
    clear a
    b = rand(10000);

2. 使用变量前，预分配内存空间

clear all
    clc
    n = 30000;
    tic;
    for k = 1:n
        a(k) = 1;
    end
    time = toc;
    disp(['未预分配内存下动态赋值长为',num2str(n),'的数组时间是:',num2str(time),'秒！'])
    
    tic
    b = zeros(1,n);
    for k = 1:n
        b(k) = 1;
    end
    time = toc;
    disp(['预分配内存下动态赋值长为',num2str(n),'的数组时间是:',num2str(time),'秒！'])
    
    %%c
    % 3. 选择恰当的数据类型
    clear all
    clc
    n = 300000;
    a = 8;
    b{1} = 8;
    c.data = 8;
    
    tic
    for k = 1:n;
        a;
    end
    time = toc;
    disp(['访问',num2str(n),'次double型数组时间是:',num2str(time),'秒！'])
    
    tic
    for k = 1:n;
        b{1};
    end
    time = toc;
    disp(['访问',num2str(n),'次cell型数组时间是:',num2str(time),'秒！'])
    
    tic
    for k = 1:n;
        c.data;
    end
    time = toc;
    disp(['访问',num2str(n),'次struct型数组时间是:',num2str(time),'秒！'])

4. 按列优先循环

clear all
    clc
    n = 1000;
    a = rand(n);
    tic
    for i = 1:n
        for j = 1:n
            a(i,j);
        end
    end
    toc
    
    for i = 1:n
        for j = 1:n
            a(j,i);
        end
    end
    toc

5. 循环次数多的变量安排在内层

clear all
    clc
    tic
    a = 0;
    for i = 1:1000
        for j = 50000
            a = a + 1;
        end
    end
    toc
    
    tic
    a = 0;
    for i = 1:50000
        for j = 1:1000
            a = a + 1;
        end
    end
    toc

6. 给一些函数“瘦身”

edit mean
    clear all
    clc
    a = rand(1,10000);
    tic
    b = mean(a)
    toc
    
    tic
    c = sum(a)/length(a)
    toc

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbnlhbndlbm1lbmc_size_16_color_FFFFFF_t_70 2][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbnlhbndlbm1lbmc_size_16_color_FFFFFF_t_70]: /images/20220223/de23a0b7055d4c9b83719efe4733a388.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbnlhbndlbm1lbmc_size_16_color_FFFFFF_t_70 1]: /images/20220223/9d1dedc4286143fcafe071710c65289c.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbnlhbndlbm1lbmc_size_16_color_FFFFFF_t_70 2]: /images/20220223/8bdf3f13c4ab492b9fe6c3f6061612b8.png