matlab基础（2）：进阶

MATLAB编程习惯与风格
变量的命名规则
Cell Mode
程序发布（Publish）
MATLAB程序调试
1. 闻道有先后，术业有专攻
所谓高手，就是他们比你更早经历了那些bug，比你经历了更多bug，仅此而已
2. 错误信息的阅读
– Index must be a positive integer or logical.
– Undefined function or variable “B”.
– Inner matrix dimensions must agree.
– Function definitions are not permitted at the prompt or in scripts.
– Index out of bounds because numel(A)=5.
– In an assignment A(I) = B, the number of elements in B and I must be the same.
– Expression or statement is incorrect–possibly unbalanced (, {, or [.
– Too many input arguments.
– ……
3. 断点调试
– 设置/清除断点
– 进入/退出调试模式
– 循环体的调试
4. 如何充分地利用网络资源？
– www.mathworks.com/matlabcentral/fileexchange/
– www.matlabsky.com
– www.ilovematlab.cn
– Some Tips:
• 再现问题(完整的错误信息、源程序文件、数据等)
• 帖子标题(应简要说明问题的本质，勿出现“跪求”、“ **大神/大侠” …)
5. 如何查看、编辑MATLAB自带的工具箱函数？
– edit
– varargin/varargout/nargin/nargout
• varargin: Variable length input argument list.
• varargout: Variable length output argument list.
• nargin: Number of input arguments specified for a function.
• nargout: Number of output arguments specified for a function.
MATLAB的内存优化配置
memory/feature memstats
禁用Java虚拟机
增加虚拟内存数量
打开系统3GB开关(32位系统)(推荐)
– “我的电脑” →“属性” →“高级” →“启动和故障恢复” →“设置” →“编辑”


向量化编程
1. 及时清除不用的变量
使用变量前，预分配内存空间
选择恰当的数据类型
循环与向量化
– 按列优先循环
– 循环次数多的变量安排在内层
给一些函数“瘦身”
……
2. 图像对象和句柄
图形对象：用于界面制作和数据可视的基本绘图元素。
图形对象是图形系统中最基本、最底层的单元。
图形对象的属性由属性名和属性值两部分组成。
句柄是图形对象的标识代码，句柄含有图形对象的各种必要的属性信息。
根屏幕的句柄为0，图形窗口的句柄为整数，其他对象的句柄为浮点数

%% I. 清空环境变量及命令% clear allclc%% II. MATLAB编程习惯与风格x_coordinate = rand(1,10);y_coordinate = rand(1,10);figureplot(x_coordinate,y_coordinate,'r-*')%% III. MATLAB程序调试% %%% % 1. Index must be a positive integer or logical.% A = [1 2 3 4 5];% A(0)% A(3.5)% A(-2)% % %%% % 2. Undefined function or variable 'B'.% B% % %%% % 3. Inner matrix dimensions must agree.% B = [1 2 3];% A * B% % %%% % 4. Function definitions are not permitted at the prompt or in scripts.% function c = add(a,b)% c = a + b;% % %%% % 5. Index out of bounds because numel(A)=5.% A(6)% % %%% % 6. In an assignment  A(I) = B, the number of elements in B and I must be the same.% A(3) = B;% % %%% % 7. Expression or statement is incorrect--possibly unbalanced (, {, or [.% mean(A(1:3)% % %%% % 8. Too many input arguments.% mean(A,1,2)%%% 9. 循环体的调试a = 1:100;b = [];for i = 21:21    index = 105 - 5*i;    b = [b a(index)];end%%% 10. 查看、编辑MATLAB自带的工具箱函数edit meanedit newff%% III. MATLAB内存优化配置feature memstats% %% IV. 向量化编程%%% 1. 及时清除不用的变量a = rand(10000);b = rand(10000);clear ab = rand(10000);%%% 2. 使用变量前，预分配内存空间clear allclcn = 30000;tic;for k = 1:n    a(k) = 1;endtime = 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！'])ticb = zeros(1,n);for k = 1:n    b(k) = 1;endtime = 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！'])%%未预分配内存下动态赋值长为30000的数组时间是:0.47359秒！预分配内存下动态赋值长为30000的数组时间是:0.0031263秒！%%%c% 3. 选择恰当的数据类型clear allclcn = 300000;a = 8;b{1} = 8;c.data = 8;ticfor k = 1:n;    a;endtime = toc;disp(['访问',num2str(n),'次double型数组时间是:',num2str(time),'秒！'])ticfor k = 1:n;    b{1};endtime = toc;disp(['访问',num2str(n),'次cell型数组时间是:',num2str(time),'秒！'])ticfor k = 1:n;    c.data;endtime = toc;disp(['访问',num2str(n),'次struct型数组时间是:',num2str(time),'秒！'])%%访问300000次double型数组时间是:0.13秒！访问300000次cell型数组时间是:0.046659秒！访问300000次struct型数组时间是:0.20081秒！%%%% 4. 按列优先循环clear allclcn = 1000;a = rand(n);ticfor i = 1:n    for j = 1:n        a(i,j);    endendtocfor i = 1:n    for j = 1:n        a(j,i);    endendtoc%%Elapsed time is 0.045155 seconds.Elapsed time is 0.081694 seconds.%%%% 5. 循环次数多的变量安排在内层clear allclctica = 0;for i = 1:1000    for j = 50000        a = a + 1;    endendtoctica = 0;for i = 1:50000    for j = 1:1000        a = a + 1;    endendtoc%%Elapsed time is 0.005826 seconds.Elapsed time is 0.214452 seconds.%%%% 6. 给一些函数“瘦身”edit meanclear allclca = rand(1,10000);ticb = mean(a)tocticc = sum(a)/length(a)toc%%b = 0.5012Elapsed time is 0.022365 seconds.c = 0.5012Elapsed time is 0.002307 seconds.%%% 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 onget(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 onplot(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 onh2 = 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')