blocks|key|1528497|text|使用内置的分析器查看代码的热门部分在哪里：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528498|profile+on
%25+some+lines+of+code
profile+off
profile+viewer|code-block|syntax|javascript|1528499|或者仅仅使用内置的tic和toc来获得快速计时：|offset|length|style|CODE|1528500|tic;
%25+some+lines+of+code
toc;|1528501|entityMap^0|0|0|9|3|D|3|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]|$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|P|$]]

Using the built-in profiler to see where the hot parts of my code are:

<pre><code>profile on
% some lines of code
profile off
profile viewer
</code></pre>

or just using the built in <code>tic</code> and <code>toc</code> to get quick timings:

<pre><code>tic;
% some lines of code
toc;
</code></pre>

blocks|key|1528456|text|使用逻辑数组直接提取满足特定条件的矩阵元素：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528457|x+=+rand(1,50)+.*+100;
xpart+=+x(+x+>+20+&+x+<+35);|code-block|syntax|javascript|1528458|现在xpart只包含x的那些在指定范围内的元素。|1528459|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Directly extracting the elements of a matrix that satisfy a particular condition, using logical arrays:

<pre><code>x = rand(1,50) .* 100;
xpart = x( x &gt; 20 &amp; x &lt; 35);
</code></pre>

Now xpart contains only those elements of x which lie in the specified range.

blocks|key|1743369|text|通过在帮助注释中添加“请参阅”行，可以快速访问其他函数文档。首先，必须在第一个注释行中包含所有大写的函数名称。做你常用的注释头内容，然后用逗号分隔的其他相关函数的列表放入SEE。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1743370|function+y+=+transmog(x)
%25TRANSMOG+Transmogrifies+a+matrix+X+using+reverse+orthogonal+eigenvectors
%25
%25+Usage:
%25+++y+=+transmog(x)
%25
%25+SEE+ALSO
%25+UNTRANSMOG,+TRANSMOG2|code-block|syntax|javascript|1743371|当您在命令行中输入"help+transmog“时，您将看到此注释标题中的所有注释，以及指向列出的其他函数的注释标题的超链接。|1743372|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Provide quick access to other function documentation by adding a "SEE ALSO" line to the help comments. First, you must include the name of the function in all caps as the first comment line. Do your usual comment header stuff, then put SEE ALSO with a comma separated list of other related functions.

<pre><code>function y = transmog(x)
%TRANSMOG Transmogrifies a matrix X using reverse orthogonal eigenvectors
%
% Usage:
% y = transmog(x)
%
% SEE ALSO
% UNTRANSMOG, TRANSMOG2
</code></pre>

When you type "help transmog" at the command line, you will see all the comments in this comment header, with hyperlinks to the comment headers for the other functions listed.

blocks|key|1528321|text|使用单个冒号将矩阵转换为向量。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528322|x+=+rand(4,4);
x(:)|code-block|syntax|javascript|1528323|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Turn a matrix into a vector using a single colon.

<pre><code>x = rand(4,4);
x(:)
</code></pre>

blocks|key|1528630|text|Vectorizing+loops。有很多方法可以做到这一点，寻找代码中的循环并看看如何将它们向量化是一件很有趣的事情。使用向量运算时，性能快得惊人！|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1528631|entityMap|0|LINK|mutability|MUTABLE|url|http://www.mathworks.com/support/tech-notes/1100/1109.html^0|0|H|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

<a href="http://www.mathworks.com/support/tech-notes/1100/1109.html" rel="noreferrer">Vectorizing loops</a>. There are lots of ways to do this, and it is entertaining to look for loops in your code and see how they can be vectorized. The performance is astonishingly faster with vector operations!

blocks|key|1529014|text|Matlab的bsxfun、arrayfun、cellfun和structfun都很有趣，而且经常省去一个循环。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1529015|M+=+rand(1000,+1000);
v+=+rand(1000,++++1);
c+=+bsxfun(@plus,+M,+v);|code-block|syntax|javascript|1529016|例如，此代码将列向量v添加到矩阵M的每一列。|1529017|但是，在应用程序的性能关键部分，您应该对这些函数进行基准测试，而不是简单的for循环，因为通常循环仍然更快。|1529018|entityMap|0|LINK|mutability|MUTABLE|url|http://www.mathworks.com/access/helpdesk/help/techdoc/ref/bsxfun.html|1|http://www.mathworks.com/access/helpdesk/help/techdoc/ref/arrayfun.html|2|http://www.mathworks.com/access/helpdesk/help/techdoc/ref/cellfun.html|3|http://www.mathworks.com/access/helpdesk/help/techdoc/ref/structfun.html^0|7|6|0|E|8|1|N|7|2|V|9|3|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]|$A|14|B|15|1|16]|$A|17|B|18|1|19]|$A|1A|B|1B|1|1C]]|C|$]]|$1|D|3|E|5|F|7|1D|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|1E|8|@]|9|@]|C|$]]|$1|K|3|L|5|6|7|1F|8|@]|9|@]|C|$]]|$1|M|3|-4|5|6|7|1G|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]|W|$5|P|Q|R|C|$S|X]]|Y|$5|P|Q|R|C|$S|Z]]]]

Matlab's <a href="http://www.mathworks.com/access/helpdesk/help/techdoc/ref/bsxfun.html" rel="noreferrer">bsxfun</a>, <a href="http://www.mathworks.com/access/helpdesk/help/techdoc/ref/arrayfun.html" rel="noreferrer">arrayfun</a>, <a href="http://www.mathworks.com/access/helpdesk/help/techdoc/ref/cellfun.html" rel="noreferrer">cellfun</a>, and <a href="http://www.mathworks.com/access/helpdesk/help/techdoc/ref/structfun.html" rel="noreferrer">structfun</a> are quite interesting and often save a loop.

<pre><code>M = rand(1000, 1000);
v = rand(1000, 1);
c = bsxfun(@plus, M, v);
</code></pre>

This code, for instance, adds column-vector v to each column of matrix M.

Though, in performance critical parts of your application you should benchmark these functions versus the trivial for-loop because often loops are still faster.

blocks|key|1743720|text|LaTeX+mode+for+formulas+in+graphs：在最近的一个版本中(R2006?)在函数调用的末尾添加额外的参数,'Interpreter','latex'，它将使用LaTeX呈现。下面是一个例子：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1743721|t=(0:0.001:1);
plot(t,sin(2*pi*[t+;+t%2B0.25]));
xlabel('t');+
ylabel('$\hat{y}_k=sin+2\pi+(t%2B{k+\over+4})$','Interpreter','latex');
legend({'$\hat{y}_0$','$\hat{y}_1$'},'Interpreter','latex');|code-block|syntax|javascript|1743722|不知道是什么时候添加的，但它可以在text()、title()、xlabel()、ylabel()、zlabel()甚至R2006b+()函数中使用图例。只需确保您所使用的语法没有歧义(因此对于legend()，您需要将字符串指定为一个单元格数组)。|1743723|entityMap|0|LINK|mutability|MUTABLE|url|http://www.mathworks.com/access/helpdesk/help/techdoc/creating_plots/f0-4741.html#f0-28104^0|1U|M|0|X|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|F|3|G|5|H|7|10|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|11|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

<a href="http://www.mathworks.com/access/helpdesk/help/techdoc/creating_plots/f0-4741.html#f0-28104" rel="nofollow noreferrer">LaTeX mode for formulas in graphs</a>: In one of the recent releases (R2006?) you add the additional arguments <code>,'Interpreter','latex'</code> at the end of a function call and it will use LaTeX rendering. Here's an example:

<pre><code>t=(0:0.001:1);
plot(t,sin(2*pi*[t ; t+0.25]));
xlabel('t'); 
ylabel('$\hat{y}_k=sin 2\pi (t+{k \over 4})$','Interpreter','latex');
legend({'$\hat{y}_0$','$\hat{y}_1$'},'Interpreter','latex');
</code></pre>

Not sure when they added it, but it works with R2006b in the text(), title(), xlabel(), ylabel(), zlabel(), and even legend() functions. Just make sure the syntax you are using is not ambiguous (so with legend() you need to specify the strings as a cell array).

blocks|key|1743292|text|下面是一个简单的例子：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1743293|我发现逗号分隔的列表语法对于构建函数调用非常有用：|1743294|%25+Build+a+list+of+args,+like+so:
args+=+{'a',+1,+'b',+2};
%25+Then+expand+this+into+arguments:
output+=+func(args{:})|code-block|syntax|javascript|1743295|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Here's a quick example:

I find the comma separated list syntax quite useful for building function calls:

<pre><code>% Build a list of args, like so:
args = {'a', 1, 'b', 2};
% Then expand this into arguments:
output = func(args{:})
</code></pre>

blocks|key|1743313|text|从Matlab调用Java代码|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1743314|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

blocks|key|1528438|text|使用nargin为可选参数设置默认值，使用nargout设置可选输出参数。快速示例|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528439|function+hLine=myplot(x,y,plotColor,markerType)
%25+set+defaults+for+optional+paramters
if+nargin<4,+markerType='none';+end
if+nargin<3,+plotColor='k';+end

hL+=+plot(x,y,'linetype','-',+...++
++++++++++++++'color',plotColor,+...
++++++++++++++'marker',markerType,+...
++++++++++++++'markerFaceColor',plotColor,'markerEdgeColor',plotColor);

%25+return+handle+of+plot+object+if+required
if+nargout>0,+hLine+=+hL;+end|code-block|syntax|javascript|1528440|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Using nargin to set default values for optional arguments and using nargout to set optional output arguments. Quick example

<pre><code>function hLine=myplot(x,y,plotColor,markerType)
% set defaults for optional paramters
if nargin&lt;4, markerType='none'; end
if nargin&lt;3, plotColor='k'; end

hL = plot(x,y,'linetype','-', ... 
 'color',plotColor, ...
 'marker',markerType, ...
 'markerFaceColor',plotColor,'markerEdgeColor',plotColor);

% return handle of plot object if required
if nargout&gt;0, hLine = hL; end
</code></pre>

blocks|key|1528905|text|我喜欢使用函数句柄的原因有很多。首先，它们是我在MATLAB中找到的最接近指针的东西，所以你可以为对象创建类似引用的行为。你也可以用它们做一些整洁(更简单)的事情。例如，替换switch语句：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528906|switch+number,
++case+1,
++++outargs+=+fcn1(inargs);
++case+2,
++++outargs+=+fcn2(inargs);
++...
end
%25
%25can+be+turned+into
%25
fcnArray+=+{@fcn1,+@fcn2,+...};
outargs+=+fcnArray{number}(inargs);|code-block|syntax|javascript|1528907|我只是觉得像这样的小东西很酷。|1528908|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I like using function handles for lots of reasons. For one, they are the closest thing I've found in MATLAB to pointers, so you can create reference-like behavior for objects. There are a few neat (and simpler) things you can do with them, too. For example, replacing a switch statement:

<pre><code>switch number,
 case 1,
 outargs = fcn1(inargs);
 case 2,
 outargs = fcn2(inargs);
 ...
end
%
%can be turned into
%
fcnArray = {@fcn1, @fcn2, ...};
outargs = fcnArray{number}(inargs);
</code></pre>

I just think little things like that are cool.

blocks|key|1528386|text|cellfun和arrayfun用于自动for循环。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528387|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

cellfun and arrayfun for automated for loops.

blocks|key|1528409|text|用于数组操作的冒号运算符。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528410|@ScottieT812提到了一个:展平数组，但还有其他所有选择数组位的变体：|1528411|x=rand(10,10);
flattened=x(:);
Acolumn=x(:,10);
Arow=x(10,:);

y=rand(100);
firstSix=y(1:6);
lastSix=y(end-5:end);
alternate=y(1:2:end);|code-block|syntax|javascript|1528412|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

The colon operator for the manipulation of arrays.

@ScottieT812, mentions one: flattening an array, but there's all the other variants of selecting bits of an array:

<pre><code>
x=rand(10,10);
flattened=x(:);
Acolumn=x(:,10);
Arow=x(10,:);

y=rand(100);
firstSix=y(1:6);
lastSix=y(end-5:end);
alternate=y(1:2:end);
</code></pre>

blocks|key|1528568|text|哦，还有反转一个数组|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528569|v+=+1:10;
v_reverse+=+v(length(v):-1:1);|code-block|syntax|javascript|1528570|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Oh, and reverse an array

<pre><code>v = 1:10;
v_reverse = v(length(v):-1:1);
</code></pre>

blocks|key|1528850|text|赋值左侧的条件参数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528851|t+=+(0:0.005:10)';
x+=+sin(2*pi*t);
x(x>0.5+&+t<5)+=+0.5;
%25+This+limits+all+values+of+x+to+a+maximum+of+0.5,+where+t<5
plot(t,x);|code-block|syntax|javascript|1528852|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

conditional arguments in the left-hand side of an assignment:

<pre><code>t = (0:0.005:10)';
x = sin(2*pi*t);
x(x&gt;0.5 &amp; t&lt;5) = 0.5;
% This limits all values of x to a maximum of 0.5, where t&lt;5
plot(t,x);
</code></pre>

blocks|key|1528965|text|了解你的axis+properties！您可以通过各种设置来调整默认绘图属性以执行您想要的操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1528966|set(gca,'fontsize',8,'linestyleorder','-','linewidth',0.3,'xtick',1:2:9);|code-block|syntax|javascript|1528967|(例如，将字体大小设置为8pt，将所有新行的线型设置为全部实线，宽度设置为0.3pt，xtick点设置为1+3+5+7+9)|1528968|Line和figure属性也很有用，但我发现自己使用最多的是axis属性。|1528969|entityMap|0|LINK|mutability|MUTABLE|url|http://www.mathworks.com/access/helpdesk/help/techdoc/ref/axes_props.html|1|http://www.mathworks.com/access/helpdesk/help/techdoc/ref/line_props.html|2|http://www.mathworks.com/access/helpdesk/help/techdoc/ref/figure_props.html^0|4|F|0|0|0|0|0|4|1|5|6|2|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]]|C|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|13|8|@]|9|@]|C|$]]|$1|K|3|L|5|6|7|14|8|@]|9|@$A|15|B|16|1|17]|$A|18|B|19|1|1A]]|C|$]]|$1|M|3|-4|5|6|7|1B|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]|U|$5|P|Q|R|C|$S|V]]|W|$5|P|Q|R|C|$S|X]]]]

Know your <a href="http://www.mathworks.com/access/helpdesk/help/techdoc/ref/axes_props.html" rel="noreferrer">axis properties</a>! There are all sorts of things you can set to tweak the default plotting properties to do what you want:

<pre><code>set(gca,'fontsize',8,'linestyleorder','-','linewidth',0.3,'xtick',1:2:9);
</code></pre>

(as an example, sets the fontsize to 8pt, linestyles of all new lines to all be solid and their width 0.3pt, and the xtick points to be [1 3 5 7 9])

<a href="http://www.mathworks.com/access/helpdesk/help/techdoc/ref/line_props.html" rel="noreferrer">Line</a> and <a href="http://www.mathworks.com/access/helpdesk/help/techdoc/ref/figure_props.html" rel="noreferrer">figure</a> properties are also useful, but I find myself using axis properties the most.

blocks|key|1529058|text|在使用min、max、mean、diff、sum、any、all等聚合函数时，请严格指定维度。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1529059|例如这一行：|1529060|reldiff+=+diff(a)+./+a(1:end-1)|code-block|syntax|javascript|1529061|可以很好地计算向量中元素的相对差异，但是，如果向量退化到只有一个元素，计算就会失败：|1529062|>>+a=rand(1,7);
>>+diff(a)+./+a(1:end-1)

ans+=
+++-0.5822+++-0.9935++224.2015++++0.2708+++-0.3328++++0.0458

>>+a=1;
>>+diff(a)+./+a(1:end-1)
???+Error+using+==>+rdivide
Matrix+dimensions+must+agree.|1529063|如果为函数指定了正确的维度，则此行将返回一个空的1+x+0矩阵，这是正确的：|1529064|>>+diff(a,+[],+2)+./+a(1,+1:end-1)

ans+=

+++Empty+matrix:+1-by-0

>>+|1529065|对于最小函数也是如此，它通常计算矩阵上的列的最小值，直到矩阵只由一行组成。-然后它将返回该行的最小值，除非维度参数另有说明，否则可能会中断您的应用程序。|1529066|我几乎可以向您保证，因此设置这些聚合函数的维度将为您节省相当多的调试工作。|1529067|至少对我来说是这样的。:)|1529068|entityMap^0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|11|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|13|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|15|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|16|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|17|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|X|$]]

Be strict with specifying dimensions when using aggregation functions like min, max, mean, diff, sum, any, all,...

For instance the line:

<pre><code>reldiff = diff(a) ./ a(1:end-1)
</code></pre>

might work well to compute relative differences of elements in a vector, however in case the vector degenerates to just one element the computation fails:

<pre><code>&gt;&gt; a=rand(1,7);
&gt;&gt; diff(a) ./ a(1:end-1)

ans =
 -0.5822 -0.9935 224.2015 0.2708 -0.3328 0.0458

&gt;&gt; a=1;
&gt;&gt; diff(a) ./ a(1:end-1)
??? Error using ==&gt; rdivide
Matrix dimensions must agree.
</code></pre>

If you specify the correct dimensions to your functions, this line returns an empty 1-by-0 matrix, which is correct:

<pre><code>&gt;&gt; diff(a, [], 2) ./ a(1, 1:end-1)

ans =

 Empty matrix: 1-by-0

&gt;&gt; 
</code></pre>

The same goes for a min-function which usually computes minimums over columns on a matrix, until the matrix only consists of one row. - Then it will return the minimum over the row unless the dimension parameter states otherwise, and probably break your application.

I can almost guarantee you that consequently setting the dimensions of these aggregation functions will save you quite some debugging work later on. 

At least that would have been the case for me. :)

blocks|key|1529168|text|为了能够快速测试函数，我像这样使用nargin：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1529169|function+result+=+multiply(a,+b)
if+nargin+==+0+%25no+inputs+provided,+run+using+defaults+for+a+and+b
++++clc;
++++disp('RUNNING+IN+TEST+MODE')
++++a+=+1;
++++b+=+2;
end

result+=+a*b;|code-block|syntax|javascript|1529170|稍后，我添加了一个单元测试脚本来针对不同的输入条件测试函数。|1529171|entityMap^0|H|6|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

In order to be able to quickly test a function, I use <code>nargin</code> like so:

<pre><code>function result = multiply(a, b)
if nargin == 0 %no inputs provided, run using defaults for a and b
 clc;
 disp('RUNNING IN TEST MODE')
 a = 1;
 b = 2;
end

result = a*b;
</code></pre>

Later on, I add a unit test script to test the function for different input conditions.

blocks|key|1743568|text|使用ismember()合并由文本标识符组织的数据。在分析不同时期的条目时很有用，在我的例子中是公司符号。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1743569|%25Merge+B+into+A+based+on+Text+identifiers
UniverseA+=+{'A','B','C','D'};
UniverseB+=+{'A','C','D'};

DataA+=+[20+40+60+80];
DataB+=+[30+50+70];

MergeData+=+NaN(length(UniverseA),2);

MergeData(:,1)+=+DataA;

[tf,+loc]+=+ismember(UniverseA,+UniverseB);

MergeData(tf,2)+=+DataB(loc(tf));

+MergeData+=

20++++30
40+++NaN
60++++50
80++++70|code-block|syntax|javascript|1743570|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Using ismember() to merge data organized by text identfiers. Useful when you are analyzing differing periods when entries, in my case company symbols, come and go.

<pre><code>%Merge B into A based on Text identifiers
UniverseA = {'A','B','C','D'};
UniverseB = {'A','C','D'};

DataA = [20 40 60 80];
DataB = [30 50 70];

MergeData = NaN(length(UniverseA),2);

MergeData(:,1) = DataA;

[tf, loc] = ismember(UniverseA, UniverseB);

MergeData(tf,2) = DataB(loc(tf));

 MergeData =

20 30
40 NaN
60 50
80 70
</code></pre>

blocks|key|1744230|text|问“为什么”(对于把我从Matlab运行时中剔除出来很有用--凌晨3点调试失败……)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1744231|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Asking 'why' (useful for jarring me out of a Matlab runtime-fail debugging trance at 3am...)

blocks|key|1528642|text|矢量化：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528643|function+iNeedle+=+findClosest(hay,needle)
%25FINDCLOSEST+find+the+indicies+of+the+closest+elements+in+an+array.
%25+Given+two+vectors+[A,B],+findClosest+will+find+the+indicies+of+the+values
%25+in+vector+A+closest+to+the+values+in+vector+B.
[hay+iOrgHay]+=+sort(hay(:)');++%25#ok+must+have+row+vector

%25+Use+histogram+to+find+indices+of+elements+in+hay+closest+to+elements+in
%25+needle.+The+bins+are+centered+on+values+in+hay,+with+the+edges+on+the
%25+midpoint+between+elements.
[iNeedle+iNeedle]+=+histc(needle,[-inf+hay%2B[diff(hay)/2+inf]]);+%25#ok

%25+Reversing+the+sorting.
iNeedle+=+iOrgHay(iNeedle);|code-block|syntax|javascript|1528644|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Vectorization:

<pre><code>function iNeedle = findClosest(hay,needle)
%FINDCLOSEST find the indicies of the closest elements in an array.
% Given two vectors [A,B], findClosest will find the indicies of the values
% in vector A closest to the values in vector B.
[hay iOrgHay] = sort(hay(:)'); %#ok must have row vector

% Use histogram to find indices of elements in hay closest to elements in
% needle. The bins are centered on values in hay, with the edges on the
% midpoint between elements.
[iNeedle iNeedle] = histc(needle,[-inf hay+[diff(hay)/2 inf]]); %#ok

% Reversing the sorting.
iNeedle = iOrgHay(iNeedle);
</code></pre>

blocks|key|1743786|text|使用sim命令直接从脚本(而不是交互)执行Simulink模型。您可以执行以下操作:从工作区变量中获取参数，并在循环中重复运行sim以模拟某些内容，同时更改参数以查看行为如何更改，并使用您喜欢的任何图形命令来绘制结果。这比试图以交互方式完成此操作要容易得多，而且在可视化结果时，它比Simulink“示波器”模块提供了更多的灵活性。(尽管您不能在模拟运行时使用它来实时查看正在发生的事情)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1743787|需要了解的一件非常重要的事情是simset命令的DstWorkspace和SrcWorkspace选项。这些控制"To+Workspace“和"From+Workspace”块获取和放置其结果的位置。Dstworkspace默认使用当前工作区(例如，如果您从函数内部调用sim，则"To+Workspace“块将显示为可从同一函数中访问的变量)，但SrcWorkspace默认使用基本工作区，如果您希望封装对sim的调用，则需要将SrcWorkspace设置为current，以便有一个干净的接口来提供/检索模拟输入参数和输出。例如：|1743788|function+Y=run_my_sim(t,input1,params)
%25+runs+"my_sim.mdl"+
%25+with+a+From+Workspace+block+referencing+I1+as+an+input+signal
%25+and+parameters+referenced+as+fields+of+the+"params"+structure
%25+and+output+retrieved+from+a+To+Workspace+block+with+name+O1.
opt+=+simset('SrcWorkspace','current','DstWorkspace','current');
I1+=+struct('time',t,'signals',struct('values',input1,'dimensions',1));
Y+=+struct;
Y.t+=+sim('my_sim',t,opt);
Y.output1+=+O1.signals.values;|code-block|syntax|javascript|1743789|entityMap|0|LINK|mutability|MUTABLE|url|http://www.mathworks.com/access/helpdesk/help/toolbox/simulink/slref/simset.html^0|2|3|1R|3|0|F|6|O|C|11|C|2S|C|3R|3|4U|C|5O|3|5Z|C|6E|7|F|6|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|C]|$9|14|A|15|B|C]|$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]]|D|@$9|1I|A|1J|1|1K]]|E|$]]|$1|H|3|I|5|J|7|1L|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|1M|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

Executing a Simulink model directly from a script (rather than interactively) using the <code>sim</code> command. You can do things like take parameters from a workspace variable, and repeatedly run <code>sim</code> in a loop to simulate something while varying the parameter to see how the behavior changes, and graph the results with whatever graphical commands you like. Much easier than trying to do this interactively, and it gives you much more flexibility than the Simulink "oscilloscope" blocks when visualizing the results. (although you can't use it to see what's going on in realtime while the simulation is running)

A really important thing to know is the <code>DstWorkspace</code> and <code>SrcWorkspace</code> options of the <a href="http://www.mathworks.com/access/helpdesk/help/toolbox/simulink/slref/simset.html" rel="nofollow noreferrer"><code>simset</code></a> command. These control where the "To Workspace" and "From Workspace" blocks get and put their results. <code>Dstworkspace</code> defaults to the current workspace (e.g. if you call <code>sim</code> from inside a function the "To Workspace" blocks will show up as variables accessible from within that same function) but <code>SrcWorkspace</code> defaults to the base workspace and if you want to encapsulate your call to <code>sim</code> you'll want to set <code>SrcWorkspace</code> to <code>current</code> so there is a clean interface to providing/retrieving simulation input parameters and outputs. For example:

<pre><code>function Y=run_my_sim(t,input1,params)
% runs "my_sim.mdl" 
% with a From Workspace block referencing I1 as an input signal
% and parameters referenced as fields of the "params" structure
% and output retrieved from a To Workspace block with name O1.
opt = simset('SrcWorkspace','current','DstWorkspace','current');
I1 = struct('time',t,'signals',struct('values',input1,'dimensions',1));
Y = struct;
Y.t = sim('my_sim',t,opt);
Y.output1 = O1.signals.values;
</code></pre>

blocks|key|1528823|text|使用[c,h]=contour和clabel(c,h,'fontsize',fontsize)绘制等高线。我通常使用fontsize参数来减小字体大小，这样数字就不会相互冲突。这对于查看2-D函数的值非常有用，而不必纠结于3D图形。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1528824|entityMap^0|2|D|G|V|1M|8|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

Contour plots with <code>[c,h]=contour</code> and <code>clabel(c,h,'fontsize',fontsize)</code>. I usually use the <code>fontsize</code> parameter to reduce the font size so the numbers don't run into each other. This is great for viewing the value of 2-D functions without having to muck around with 3D graphs.

blocks|key|1744282|text|运行在线算法时使用persistent+(静态)变量。它可以加速贝叶斯机器学习等领域的代码，在这些领域中，模型针对新样本进行迭代训练。例如，为了计算独立的对数似然，我最初从头开始计算对数似然，并通过将这个先前计算的对数似然与附加的对数似然相加来更新它。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1744283|不是给出更专业的机器学习问题，而是让我给出一个通用的在线平均代码，我取了from+here|1744284|function+av+=+runningAverage(x)
%25+The+number+of+values+entered+so+far+-+declared+persistent.
persistent+n;
%25+The+sum+of+values+entered+so+far+-+declared+persistent.
persistent+sumOfX;
if+x+==+'reset'+%25+Initialise+the+persistent+variables.
++++n+=+0;
++++sumOfX+=+0;
++++av+=+0;
else+%25+A+data+value+has+been+added.
++++n+=+n+%2B+1;
++++sumOfX+=+sumOfX+%2B+x;
++++av+=+sumOfX+/+n;+%25+Update+the+running+average.
end|code-block|syntax|javascript|1744285|然后，调用将产生以下结果|1744286|runningAverage('reset')
ans+=+0
>>+runningAverage(5)
ans+=+5
>>+runningAverage(10)
ans+=+7.5000
>>+runningAverage(3)
ans+=+6
>>+runningAverage('reset')
ans+=+0
>>+runningAverage(8)
ans+=+8|1744287|entityMap|0|LINK|mutability|MUTABLE|url|http://www.mathworks.com/help/techdoc/ref/persistent.html|1|http://undergraduate.csse.uwa.edu.au/units/CITS1005/lectures/topic10.pdf^0|9|A|9|A|0|0|10|9|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|6|7|16|8|@]|D|@$9|17|A|18|1|19]]|E|$]]|$1|H|3|I|5|J|7|1A|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1B|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|1C|8|@]|D|@]|E|$K|L]]|$1|Q|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]|Y|$5|T|U|V|E|$W|Z]]]]

Using <a href="http://www.mathworks.com/help/techdoc/ref/persistent.html" rel="nofollow"><code>persistent</code></a> (static) variables when running an online algorithm. It may speed up the code in areas like Bayesian machine learning where the model is trained iteratively for the new samples. For example, for computing the independent loglikelihoods, I compute the loglikelihood initially from scratch and update it by summing this previously computed loglikelihood and the additional loglikelihood. 

Instead of giving a more specialized machine learning problem, let me give a general online averaging code which I took <a href="http://undergraduate.csse.uwa.edu.au/units/CITS1005/lectures/topic10.pdf" rel="nofollow">from here</a>:

<pre><code>function av = runningAverage(x)
% The number of values entered so far - declared persistent.
persistent n;
% The sum of values entered so far - declared persistent.
persistent sumOfX;
if x == 'reset' % Initialise the persistent variables.
 n = 0;
 sumOfX = 0;
 av = 0;
else % A data value has been added.
 n = n + 1;
 sumOfX = sumOfX + x;
 av = sumOfX / n; % Update the running average.
end
</code></pre>

Then, the calls will give the following results

<pre><code>runningAverage('reset')
ans = 0
&gt;&gt; runningAverage(5)
ans = 5
&gt;&gt; runningAverage(10)
ans = 7.5000
&gt;&gt; runningAverage(3)
ans = 6
&gt;&gt; runningAverage('reset')
ans = 0
&gt;&gt; runningAverage(8)
ans = 8
</code></pre>

blocks|key|1529119|text|-You可以创建一个名为Startupp.m的初始化文件的Matlab快捷方式。在这里，我为我的Matlab会话定义了格式、输出精度和绘图参数(例如，我使用较大的绘图轴/字体大小，这样当我将.fig放入演示文稿时就可以清楚地看到它们。)查看其中一位开发人员关于它的很好的博客文章http://blogs.mathworks.com/loren/2009/03/03/whats-in-your-startupm/。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1529120|-You可以使用"+load“函数加载整个数值型ascii文件。这并不是特别快，但很快就完成了原型的工作(这不应该是Matlab的座右铭吗？)|1529121|-As提到过，冒号运算符和矢量化是救命稻草。螺丝圈。|1529122|entityMap|0|LINK|mutability|MUTABLE|url|http://blogs.mathworks.com/loren/2009/03/03/whats-in-your-startupm/^0|3V|1V|0|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@$A|Q|B|R|1|S]]|C|$]]|$1|D|3|E|5|6|7|T|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|U|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]]]

-You can make a Matlab shortcut to an initialization file called startup.m. Here, I define formatting, precision of the output, and plot parameters for my Matlab session (for example, I use a larger plot axis/font size so that .fig's can be seen plainly when I put them in presentations.) See a good blog post from one of the developers about it <a href="http://blogs.mathworks.com/loren/2009/03/03/whats-in-your-startupm/" rel="nofollow noreferrer">http://blogs.mathworks.com/loren/2009/03/03/whats-in-your-startupm/</a> .

-You can load an entire numerical ascii file using the "load" function. This isn't particularly fast, but gets the job done quickly for prototyping (shouldn't that be the Matlab motto?)

-As mentioned, the colon operator and vectorization are lifesavers. Screw loops.

blocks|key|1529404|text|下面是我经常使用的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1529405|+`%25+useful+abbreviations`|code-block|syntax|javascript|1529406|flat=@(x)+x(:);

%25+print+basic+statistics
stats=@(x)+sprintf('mean+%2B/-+s.d.+\t=+%25f+%2B/-+%25f\nmin,+max+\t\t=+%25f,+%25f\nmedian,+mode+\t=+%25f,+%25f',+...
++++mean(flat(x)),+std(flat(x)),+min(flat(x)),+max(flat(x)),+median(flat(x)),+mode(flat(x))+);

nrows=@(x)+size(x,1);
ncols=@(x)+size(x,2);
nslices=@(x)+size(x,3);

%25+this+is+just+like+ndims+except+it+returns+0+for+an+empty+matrix+and
%25+ignores+dimensions+of+size+0.
ndim=@(x)+length(find(size(x)));|1529407|​|1529408|这些缩写对于查找图像小区域中像素值的平均值和标准差很有用。我将使用以下逻辑：|1529409|+`phantomData+=+phantom();`|1529410|stats(+phantomData(50:80,+50:80)+)|1529411|1529412|如果我想在标题中添加图像的大小，该怎么办？|1529413|+`imagesc(+phantomData+);`|1529414|title(+sprintf('The+image+size+is+%25d+by+%25d+by+%25d.',+nrows(phantomData),+ncols(phantomData),+nslices(phantomData))+)|1529415|1529416|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|D|7|12|8|@]|9|@]|A|$E|F]]|$1|I|3|J|5|6|7|13|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|14|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|Q|3|J|5|6|7|17|8|@]|9|@]|A|$]]|$1|R|3|S|5|6|7|18|8|@]|9|@]|A|$]]|$1|T|3|U|5|D|7|19|8|@]|9|@]|A|$E|F]]|$1|V|3|W|5|D|7|1A|8|@]|9|@]|A|$E|F]]|$1|X|3|J|5|6|7|1B|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]]|Z|$]]

Here's what I use frequently:

<code>
 % useful abbreviations

<pre><code>flat=@(x) x(:);

% print basic statistics
stats=@(x) sprintf('mean +/- s.d. \t= %f +/- %f\nmin, max \t\t= %f, %f\nmedian, mode \t= %f, %f', ...
 mean(flat(x)), std(flat(x)), min(flat(x)), max(flat(x)), median(flat(x)), mode(flat(x)) );

nrows=@(x) size(x,1);
ncols=@(x) size(x,2);
nslices=@(x) size(x,3);

% this is just like ndims except it returns 0 for an empty matrix and
% ignores dimensions of size 0.
ndim=@(x) length(find(size(x)));
</code></pre>

</code>

These abbreviations are useful for finding the mean and standard deviation of pixel values in a small area of an image. I would use the following logic:

<code>
 phantomData = phantom();

<pre><code>stats( phantomData(50:80, 50:80) )
</code></pre>

</code>

What if I wanted to put the size of an image in its title?

<code>
 imagesc( phantomData );

<pre><code>title( sprintf('The image size is %d by %d by %d.', nrows(phantomData), ncols(phantomData), nslices(phantomData)) )
</code></pre>

</code>

I think everyone would agree that the MATLAB language is not pretty, or particularly consistent. But nevermind! We still have to use it to get things done.

What are your favourite tricks for making things easier? Let's have one per answer so people can vote them up if they agree. Also, try to illustrate your answer with an example.

What is your favourite MATLAB/Octave programming trick?

我想每个人都会同意，MATLAB语言并不美观，也不是特别一致。但不要紧！我们仍然需要用它来完成任务。你最喜欢的让事情变得更简单的技巧是什么？让我们每个答案一个，这样人们可以投票支持他们，如果他们同意。另外，试着用一个例子来说明你的答案。

问你最喜欢的MATLAB/Octave编程技巧是什么？
EN

回答 26

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问你最喜欢的MATLAB/Octave编程技巧是什么？
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