MATLAB:是否可以在本机构造(单元、结构等)上重载运算符? [英] MATLAB: Is it possible to overload operators on native constructs (cells, structs, etc)?

问题描述

我正在使用单元格来管理我正在处理的某些内容中的数据.我希望能够执行以下操作:

I'm using cells to manage data in some stuff I'm working on. I'd like to be able to do things like:

A = cellfun( @(X)( randn( 5,5 ) ), cell( 5,1 ), 'UniformOutput', 0 );
B = cellfun( @(X)( randn( 5,5 ) ), cell( 5,1 ), 'UniformOutput', 0 );
%#
%# Each of the following would fail if cell member dimensions
%# don't match up
%#
%# matrix sums for each cell entry
%# C = A + B;
C = cellfun( @(X,Y)( X + Y ), A, B, 'UniformOutput', 0 );
%#
%# direct/hadamard product
%# D = A .* B;
D = cellfun( @(X,Y)( X .* Y ), A, B, 'UniformOutput', 0 );
%#
%# matrix-matrix products (not across all entries)
%# E = A * B;
E = cellfun( @(X,Y)( X * Y ), A, B, 'UniformOutput', 0 );

但是，我不希望使用极其冗长的语法来做这件事.当我只想为单元格上的数学运算符提供定义时，为此创建一个新类似乎有点过分.

However, I don't want the extremely verbose syntax to do it. It seems a bit overboard to create a new class for this when all I want to do is provide a definition for math operators on cells.

问题:上课是唯一的途径吗?

The question: Is a class the only way to go about it?

如果我写一个类来做到这一点，它肯定会让编写代码更容易.我看到的最大的负面影响与优化有关，尽管还有一些其他问题让我感到困扰..

If I write a class to do this, it certainly makes it easier to write the code. The biggest negatives I see are related to optimizations, though there's a few other things that bug me about it..

在幕后进行的任何优化(例如，当 Jacket 编译某些东西以在 GPU 上运行时)可能会更难确定要进行哪些优化.例如，假设我有两个单元格 (A,B)，其中包含许多适当维度的矩阵.如果我编写代码来生成一个新单元格:

Any optimizations going on behind the scenes (eg, when Jacket compiles something to run on a GPU) would potentially have a harder time determining what optimizations to make. As an example, suppose I have two cells (A,B) containing a number of matrices of appropriate dimension. If I write code to produce a new cell:

Z = c1*A + c2*B

... 使用标量 {c1,c2}，我可以这样写，Jacket(或其他任何东西)很容易确定它应该按以下方式进行计算:

... with scalars {c1,c2}, I can write it in such a way that Jacket (or whatever) will easily determine that it should do the calculations as:

Z{kk} = c1*A{kk} + c2*B{kk}

或者可能是比这更好的优化.除此以外.它最终可能会变得更慢和/或内存效率更低，例如:

or perhaps an even better optimization than that. Otherwise. it may end up with something slower and/or less memory efficient, eg:

temp1 = cellfun( @(X)( c1*X ), A );
temp2 = cellfun( @(X)( c2*X ), B );
Z     = cellfun( @plus, temp1, temp2 );

假设 MATLAB 或 Jacket 无法对其进行优化，这最终会占用过多内存.

Assuming MATLAB or Jacket are unable to optimize it, this would end up using too much memory.

推荐答案

实际上可以为 MATLAB 中的内置数据类型创建新的运算符或重载现有的运算符.我在我的回答中描述了一个关于修改整数类型的默认溢出行为.

It is in fact possible to create new operators or overload existing ones for built-in data types in MATLAB. I describe one example of this in my answer to another SO question about modifying the default overflow behavior of integer types.

首先，您可能想查看当前存在哪些用于元胞数组的方法.您可以使用函数 METHODS 来做到这一点，这就是我得到的在 MATLAB R2010b 中:

First, you may want to look at what methods currently exist for cell arrays. You can do this using the function METHODS, and here's what I get in MATLAB R2010b:

>> methods cell

Methods for class cell:

aa2nt            issorted         regexptranslate  strfind          
accumarray       newdepfun        reshape          strjust          
cell2struct      nt2aa            rna2dna          strmatch         
ctranspose       nwalign          seq2regexp       strtok           
display          permute          setdiff          transpose        
dna2rna          regexp           setxor           union            
intersect        regexpi          sort             unique           
ismember         regexprep        strcat           

算术运算符方法将在上面的列表中显示为它们的 函数等效项，例如 + 运算符的 plus 或 .* 运算符的 times.仅为元胞数组定义了 transpose 方法(.' 运算符).您必须自己创建其余部分，定义给定运算符对元胞数组参数的行为方式.

The arithmetic operator methods would show up in the above list as their function equivalents, like plus for the + operator or times for the .* operator. Only the transpose method (.' operator) is defined for cell arrays. You would have to create the rest yourself, defining how a given operator will behave for cell arrays arguments.

您可以首先创建一个名为 @cell 的新文件夹并将其放置在您的 MATLAB 路径.然后将新方法放在 @cell 文件夹中.例如，对于元胞数组(没有任何输入检查、错误检查等)的 plus 方法的非常实现是这样的:

You can do this by first making a new folder called @cell and placing it in an existing folder on your MATLAB path. You would then place your new methods in the @cell folder. For example, a very simple implementation of a plus method for cell arrays (without any input-checking, error-checking, etc.) would be this:

function C = plus(A,B)
  C = cellfun(@plus,A,B,'UniformOutput',false);  %# Apply plus cell-wise
end

在上面的代码中，您可能首先要检查操作数 A 和 B 是否是相同大小的元胞数组.但是，您可以创建任何您想要的独特功能，例如允许 B 成为一个标量值，它会被添加到 A 的每个单元格中.完全由您来定义 + 运算符对元胞数组的行为.

In the above code, you would probably first want to check that the operands A and B are cell arrays of the same size. However, you could create whatever unique functionality you want, such as allowing B to be a scalar value which would get added to every cell of A. It's totally up to you to define how the + operator will behave for cell arrays.

这将允许您以更紧凑的方式编写代码，如下例所示:

This would then allow you to write your code in a much more compact way, as in this example:

>> A = {[1 2 3] [4 5] 6};  %# One 3-element cell array
>> B = {5 [4 5] 2};        %# Another 3-element cell array
>> C = A+B;                %# Use the new plus operator
>> C{:}                    %# Display the cell contents

ans =

     6     7     8

ans =

     8    10

ans =

     8

我无法真正谈论幕后优化以及这可能会如何影响它们.我知道文档 提高性能的技术"提到了关于重载内置函数:

I can't really speak to the behind-the-scenes optimizations and how this might affect them. I know that the documentation "Techniques for Improving Performance" specifically mentions this about overloading built-in functions:

重载 MATLAB 内置函数在任何标准 MATLAB 数据上课程可能会产生负面影响表现.例如，如果你重载 plus 函数来处理任何整数类不同的是，你可能会阻碍某些MATLAB 内置优化plus 的函数代码，因此可以减慢任何使用的程序这种过载.

Overloading MATLAB built-in functions on any of the standard MATLAB data classes can negatively affect performance. For example, if you overload the plus function to handle any of the integer classes differently, you may hinder certain optimizations in the MATLAB built-in function code for plus, and thus may slow down any programs that make use of this overload.

但是，在您的情况下，您没有为类重载现有函数.您只是为该类创建了不存在的新类，因此很难说这最终会对性能产生什么影响.

However, in your case you aren't overloading existing functions for a class. You're simply creating new ones that didn't exist for that class, so it's hard to say what effect this may ultimately have on performance.

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