matlab、2

%% I. 清空环境变量及命令    clear all    clc%% II. MATLAB编程习惯与风格    x_coordinate = rand(1,10);    y_coordinate = rand(1,10);    figure    plot(x_coordinate,y_coordinate,'r-*')%  循环体的调试    a = 1:100;    b = [];    for i = 21:21        index = 105 - 5*i;        b = [b a(index)];    end%%% 查看、编辑MATLAB自带的工具箱函数    edit mean    edit newff%% IV. 向量化编程%%% 1. 及时清除不用的变量    a = rand(10000);    b = rand(10000);    clear a    b = rand(10000);%%% 2. 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%%% 3. 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%%% 4. 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%% V. 图像对象和句柄%%% 1. 如何设置线条的属性呢？    x = 0:0.01:2*pi;    y = sin(x);    h = plot(x,y);    grid on    get(h)    set(h,'linestyle','-','linewidth',2,'color','k')% 2. 如何修改网格的间隔呢？      set(gca,'xtick',0:0.5:7)    set(gca,'ytick',-1:0.1:1)% 3. 如何设置图例的字体及大小呢？    x = 0:0.01:2*pi;    y1 = sin(x);    y2 = cos(x);    plot(x,y1,'r')    hold on    plot(x,y2,'-.b')    h = legend('sin(x)','cos(x)');    set(h,'fontsize',16,'color','k','edgecolor','r','textcolor','w')%%% 4. 如何拆分图例呢？    x = 0:0.01:2*pi;    y1 = sin(x);    y2 = cos(x);    h1 = plot(x,y1,'r');    hold on    h2 = plot(x,y2,'-.b');    ax1 = axes('position',get(gca,'position'),'visible','off');    legend(ax1,h1,'sin(x)','location','northwest')    ax2 = axes('position',get(gca,'position'),'visible','off');    legend(ax2,h2,'cos(x)','location','northeast')