matlab常见问题.txt

matlab常见问题集,不错的资料哦,MATLAB初学者很有帮助

           An elegant chunk of code to perform least-squares circle fitting 
        was written by Bucher Izhak and has been floating around the 
        newgroup for some time.  The first reference to it that I can 
        find is in:

                 function [xc,yc,R,a] = circfit(x,y)
                 %CIRCFIT  Fits a circle in x,y plane
                 %
                 % [XC, YC, R, A] = CIRCFIT(X,Y)
                 % Result is center point (yc,xc) and radius R.A is an 
                 % optional output describing the circle's equation:
                 %
                 %   x^2+y^2+a(1)*x+a(2)*y+a(3)=0
 
                 % by Bucher izhak 25/oct/1991
 
                 n=length(x);  xx=x.*x; yy=y.*y; xy=x.*y;
                 A=[sum(x) sum(y) n;sum(xy) sum(yy)...
                    sum(y);sum(xx) sum(xy) sum(x)];
                 B=[-sum(xx+yy) ; -sum(xx.*y+yy.*y) ; -sum(xx.*x+xy.*y)];
                 a=A\B;
                 xc = -.5*a(1);
                 yc = -.5*a(2);
                 R  =  sqrt((a(1)^2+a(2)^2)/4-a(3));

           Tom Davis provided a more sophisticated approach that works 
        for more cases in  and Code included.


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8)Matlab中如何绘制箭头？
:#FangQ([e-mail]),2002/6/21, SMTH/MathTools #

        到http://www.mathworks.com/matlabcentral/fileexchange/index.jsp
        2-D Plotting and Graphics中查找arrow.m，或者
        http://www.mathworks.com/matlabcentral/spotlight/arrows.shtml
        http://www.math.umd.edu/~jec/matcomp/matcompmfiles/mfiles.html


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9)Matlab中如何作二维数据的插值?
:#FangQ([e-mail]),2002/6/21, BigGreen/MathTools #


        对于一维、二维、三维规则数据点阵使用interp1/interp2/interp3，
        二维、三维非规则数据用griddata/griddata3


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10)Matlab中如何绘制三维数据阵？
:#FangQ([e-mail]),2002/6/21, BigGreen/MathTools #


        如果使用matlab，打开帮助窗口，在目录树上找到
        MATLAB\Using Matlab\
           3-D Visualization: Volume Visualization Techniques
           
        如果图形复杂，建议使用Tecplot，参见Tecplot手册中数据格式，将你
        的三维数据读入Tecplot，双击zone，可以设置mesh/contour/surface 
        transparency等。
        
        在Field菜单中有3D Iso-surface Details和3D Slice Details，可以绘制等值

        面和任意平面的截面图。


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11)Matlab中如何注解一大段代码？
:#hyphone,2002/7/6, SMTH/MathTools #

        注释大段代码选中代码，Ctrl+R；取消注释，选中代码，Ctrl+T。
        或者用Edit菜单或者右键弹出中的注释。

:#misc,2002/6/21, SMTH/MathTools #

        if(0)
        大段的代码
        end


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12)Matlab中如何计算程序运行的时间？
:#misc,2002/6/21, SMTH/MathTools #

        tic
          your_code;
        toc
        或者使用
        t=cputime; 
          your_operation; 
        cputime-t


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13)Matlab中如何改变默认的工作路径？
:#SindyGong, 2002/4/7, SMTH/MathTools #

        编辑一个startup.m文件，其中cd yourpath
        或者在X:\matlab\toolbox\local\matlabrc.m的最后添加cd yourpath
        参见：
        http://www.mathworks.com/support/solutions/data/25164.shtml


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14)Matlab如何改变默认的图形字体?
:#comp.soft-sys.matlab FAQ#

        编辑一个startup.m文件，其中
        set(0,'DefaultObjectnamePropertyName',Value)
        或者在X:\matlab\toolbox\local\matlabrc.m的最后添加
        set(0,'DefaultObjectnamePropertyName',Value)


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15)如何在Matlab中实现交互操作？
:#FangQ([e-mail]),2002/6/21,BigGreen/MathTools #


        如果只在命令窗口进行交互操作，请参见demo中的例子，主要是
        通过input命令和pause/clear/disp等实现的，还有一些窗口资源可以使
        用：
        uigetfile,uiputfile,uiwait,uisetcolor,uisetfont, uiopen,uisave
        inputdlg,msgbox,helpdlg,questdlg,warndlg,errordlg


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16)Matlab中为什么只能在小数点后显示四位?
:#FangQ([e-mail]),2002/6/21,BigGreen/MathTools #


        用format命令来改变命令窗口数字的显示格式和精度，但不会影
        响matlab的计算精度，matlab的矩阵运算默认都是双精度浮点型运算。



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17)Matlab如何在命令窗口按照格式输出？
:#FangQ([e-mail]),2002/6/21,SMTHTools #

        fprintf(1,"your_format_string",var1,var2,…);


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18)如何在Matlab中画隐函数曲线？
:#FangQ([e-mail]),2002/6/21,BigGreen/MathTools #


        在http://www.mathworks.com/matlabcentral/fileexchange/index.jsp
        查找implicit，会找到一个Arthur Jutan写的implot.m
        Mathematica中绘制隐函数用ImplicitPlot[]
        或者ImplicitPlot3D[]
        Maple中为implicitplot(),implicitplot3d()
        参见
        http://engineering.dartmouth.edu/~fangq/MATH/download/source/
         ImplicitPlot3D.htm


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19)Matlab中什么函数可以删除矩阵的某一行或列？
:#FangQ([e-mail]),2002/6/21,BigGreen/MathTools #


        A(j,:)=[];  %删除A的第j行
        A(:,i)=[];  %删除A的第i列


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20)Matlab中能开的最大数组是由什么决定的？
:# chenft (mike),2002/6/1, SMTH/MathTools #

      I have had similar problems. Below is an explanation I received from  
      Ian Boyd 
      from Mathworks (just giving credit where credit is due) that explains 
      what's happening. You solution is to run matlab with the -nojvm mode.
      "The heap memory system in JAVA consists of data and handle elements. 
      When you allocate a variable you get a handle and data. As long as  
      data has an associated handle, the JVM considers it valid and 
      will not clean it up.

      However, when you call the clear function in MATLAB, all handles are 
      destroyed, and the data associated is now invalid. This means that  
      the JAVA engine can free up that data (garbage collection), but does 
      not mean that it will clean it up at that moment.

      Calling the PACK command encourages JAVA to run the garbage collector 
      and de-fragment the memory. But it does not force it to (This is part  

      of the JAVA design). Even though the memory is 'freed' on the heap,  
      it is not actually free to the OS, it is only free to the JVM. Here  
      is one way to think of it:

      [MATLAB]
      [JAVA]
        [OS]
      MATLAB runs on JAVA (virtual machine), and Java runs on the OS 
      (physical machine). So when MATLAB is running in JAVA mode memory 
      allocations  are requested from the JRE, not the OS.

      One problem you may be running into is that the default maximum 
      JAVA heap size is relatively low ( <= 64 MB), so that is all the 
      memory one session of MATLAB will ever get on your system.

      The good news is that you can increase this value. You will need 
      to create a java.opts file in $MATLAB/bin/$ARCH (or in the current 
      directory when  you start MATLAB) and put the following command:

      %%%BEGIN CODE%%%
      maxHeapSize = 268435456
      %%%END CODE%%%

      This will give you 256MB of JVM memory and you can adjust the 
      parameter as needed.

      Note: $MATLAB is the root directory and $ARCH is your system
      architecture. This solution works on Windows as well as Solaris, 
      Linux,Alpha, and SGI. A similar operation is possible on IBM and 
      HPUX, but with a different syntax.

      For the 1.1.8 JVM (Windows, Linux, Solaris, Alpha, SGI) our 
      defaults are:
      
         minHeapSize = 16000000
         maxHeapSize = 64000000

      These are the structure field names in  that correspond to 
      -ms and -mx, and the settings above are roughly 16MB and 64MB.
      To investigate the Java heap a bit, ask via the following:
         >> java.lang.Runtime.getRuntime.totalMemory
         >> java.lang.Runtime.getRuntime.freeMemory

      When the free memory hits zero, Java will double the heap size 
      (up to the maximum setting).

      If you choose to run without Java, you will remove the overhead 
      of the middle man, but you will also lose some MATLAB functionality 
      (mostly graphics and the Editor). You will still have most 
      of the computational power though.

      Without JAVA, memory management will come directly from the OS, 
      and a CLEAR operation will result in memory being freed back to 
      the OS.


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21)如何在Matlab中添加新的工具箱？
:#FangQ([e-mail]),2002/6/21,BigGreen/MathTools #


        如果是Matlab安装光盘上的工具箱，重新执行安装程序，选中即可。
        如果是单独下载的工具箱，一般情况下仅需要把新的工具箱解压到某
        个目录，然后用addpath(对于多个目录的使用genpath())或者pathtool添
        加工具箱的路径，然后用which newtoolbox_command.m来检验是否可
        以访问。如果能够显示新设置的路径，则表明该工具箱可以使用了。
        具体请看工具箱自己代的README文件。



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22)如何读写Matlab的.mat文件？
:#FangQ([e-mail]),2002/6/21,BigGreen/MathTools #


        文件结构参见：
        http://www.mathworks.de/access/helpdesk/help/pdf_doc/matlab/
          matfile_format.pdf
        http://www.mathworks.com/support/solutions/data/8757.shtml
        ftp://ftp.mathworks.com/pub/tech-support/solutions/s8757/
          readmemat.txt

        建议使用matlab自己提供的函数来读写简单安全，或者参考：
        http://engineering.dartmouth.edu/~fangq/MATH/download/
           source/mat_file.txt
        来自matlab的c math library


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23)如何得到contour线上的坐标点？
:#FangQ([e-mail]),2002/6/21,BigGreen/MathTools #


        lcount=5;
        [c,h]=contour(peaks,lcount);
        x=get(h,'xdata');
        y=get(h,'ydata');

        这里得到的x和y都是cell数组，用x{1}/y{1}来得到每条线上的坐标对，
        注意，每条线的最后一个数据是NaN


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24)如何将Matlab绘制的三维网格图帖到word里？
:#FangQ([e-mail]),2002/6/21,BigGreen/MathTools #


        如果需要位图，好处是所见即所得，坏处是图像精度差，不能放缩：
                1.用拷屏 Alt+PrintScreen
                2.在图形窗口菜单Edit\Copy Options….\选择Bitmap，可以
                  选择透明背景，然后Edit\Copy Figure

        如果需要拷贝矢量图：
                在图形窗口菜单Edit\Copy Options….\选择Metafile,然后
                Edit\Copy Figure，在Word中粘贴

        经常地，按照Metafile方式粘贴的图片曲线会出现锯齿，最好的方式是
        使用eps文件：
                1.将需要拷贝的图作为当前窗口
                2.再转换到matlab命令窗口，print -deps filename.eps
                3.-deps还可以用depsc,deps2,depsc2
                4.在word中插入图片，选中该eps，如果是word 2000以前版本