最近项目中需要使用MATLAB优秀的矩阵计算功能，然后再把矩阵保存到文件中，供其他语言的程序使用。这就需要把矩阵保存成文件格式，而不是mat形式。这里主要使用到了三种方法： by木子肖子
1. dlmwrite: 写ASCII编码的有分隔符的矩阵。
function dlmwrite(filename, m, varargin)
%DLMWRITE Write ASCII delimited file.
%
% DLMWRITE('FILENAME',M) writes matrix M into FILENAME using ',' as the
% delimiter to separate matrix elements.
%
% DLMWRITE('FILENAME',M,'DLM') writes matrix M into FILENAME using the
% character DLM as the delimiter.
%
% DLMWRITE('FILENAME',M,'DLM',R,C) writes matrix M starting at
% offset row R, and offset column C in the file. R and C are zero-based,
% so that R=C=0 specifies the first value in the file.
%
% DLMWRITE('FILENAME',M,'ATTRIBUTE1','VALUE1','ATTRIBUTE2','VALUE2'...)
% An alternative calling syntax that uses attribute value pairs for
% specifying optional arguments to DLMWRITE. The order of the
% attribute-value pairs does not matter, as long as an appropriate value
% follows each attribute tag.
%
% DLMWRITE('FILENAME',M,'-append') appends the matrix to the file.
% without the flag, DLMWRITE overwrites any existing file.
%
% DLMWRITE('FILENAME',M,'-append','ATTRIBUTE1','VALUE1',...)
% Is the same as the previous syntax, but accepts attribute value pairs,
% as well as the '-append' flag. The flag can be placed in the argument
% list anywhere between attribute value pairs, but not between an
% attribute and its value.
%
% USER CONFIGURABLE OPTIONS
%
% ATTRIBUTE : a quoted string defining an Attribute tag. The following
% attribute tags are valid -
% 'delimiter' => Delimiter string to be used in separating matrix
% elements.
% 'newline' => 'pc' Use CR/LF as line terminator
% 'unix' Use LF as line terminator
% 'roffset' => Zero-based offset, in rows, from the top of the
% destination file to where the data it to be
% written.
% 'coffset' => Zero-based offset, in columns, from the left side
% of the destination file to where the data is to be
% written.
% 'precision' => Numeric precision to use in writing data to the
% file, as significant digits or a C-style format
% string, starting with '%', such as '%10.5f'. Note
% that this uses the operating system standard
% library to truncate the number.
%
%
% EXAMPLES:
%
% DLMWRITE('abc.dat',M,'delimiter',';','roffset',5,'coffset',6,...
% 'precision',4) writes matrix M to row offset 5, column offset 6, in
% file abc.dat using ; as the delimiter between matrix elements. The
% numeric precision is of the data is set to 4 significant decimal
% digits.
%
% DLMWRITE('example.dat',M,'-append') appends matrix M to the end of
% the file example.dat. By default append mode is off, i.e. DLMWRITE
% overwrites the existing file.
%
% DLMWRITE('data.dat',M,'delimiter','\t','precision',6) writes M to file
% 'data.dat' with elements delimited by the tab character, using a precision
% of 6 significant digits.
%
% DLMWRITE('file.txt',M,'delimiter','\t','precision','%.6f') writes M
% to file file.txt with elements delimited by the tab character, using a
% precision of 6 decimal places.
%
% DLMWRITE('example2.dat',M,'newline','pc') writes M to file
% example2.dat, using the conventional line terminator for the PC
% platform.
%
% See also DLMREAD, CSVWRITE, NUM2STR, SPRINTF.
% Brian M. Bourgault 10/22/93
% Modified: JP Barnard, 26 September 2002.
% Michael Theriault, 6 November 2003
% Copyright 1984-2011 The MathWorks, Inc.
%-------------------------------------------------------------------------------
给定矩阵M，以读者指定的分隔符将矩阵写入文件中，可以按照C语言的形式控制写入数字的形式，如’%u‘表示整形，’%5.6f‘表示5位整数6位小数的浮点型。
此方法按矩阵的行对数字进行格式调整，并一行一行的写入文件中，效率较慢，我测试了行10^7，列2的矩阵，用了880s。
2.num2str,然后再fprintf，先将矩阵转化为字符串，然后在fprinf写入矩阵。
%NUM2STR Convert numbers to a string. % T = NUM2STR(X) converts the matrix X into a string representation T % with about 4 digits and an exponent if required. This is useful for % labeling plots with the TITLE, XLABEL, YLABEL, and TEXT commands. % % T = NUM2STR(X,N) converts the matrix X into a string representation % with a maximum N digits of precision. The default number of digits is % based on the magnitude of the elements of X. % % T = NUM2STR(X,FORMAT) uses the format string FORMAT (see SPRINTF for % details). % % Example 1: % num2str(randn(2,2),3) produces a string matrix such as % % 1.44 -0.755 % 0.325 1.37 % % Example 2: % num2str(rand(2,3) * 9999, '%10.5e\n') produces a string matrix % such as % % 8.14642e+03 % 1.26974e+03 % 6.32296e+03 % 9.05701e+03 % 9.13285e+03 % 9.75307e+02 % % See also INT2STR, SPRINTF, FPRINTF, MAT2STR. % Copyright 1984-2012 The MathWorks, Inc. %------------------------------------------------------------------------------
num2str将矩阵转化为字符串，效率和int2str差不多，比mat2str快很多。num2str也可以按照C语言的形式控制数字转化为字符串的形式。转化时是以列为单位进行的。效率挺快，转化行10^7，列2的矩阵不到1s.生成的内存大约是原矩阵的2倍左右，但中间过程占用内存较大，对于较大的矩阵可以考虑分块转化。然后就是是将字符用fprintf写入文件了。
3.fprintf函数
%FPRINTF Write formatted data to text file.
% FPRINTF(FID, FORMAT, A, ...) applies the FORMAT to all elements of
% array A and any additional array arguments in column order, and writes
% the data to a text file. FID is an integer file identifier. Obtain
% FID from FOPEN, or set it to 1 (for standard output, the screen) or 2
% (standard error). FPRINTF uses the encoding scheme specified in the
% call to FOPEN.
%
% FPRINTF(FORMAT, A, ...) formats data and displays the results on the
% screen.
%
% COUNT = FPRINTF(...) returns the number of bytes that FPRINTF writes.
%
% FORMAT is a string that describes the format of the output fields, and
% can include combinations of the following:
%
% * Conversion specifications, which include a % character, a
% conversion character (such as d, i, o, u, x, f, e, g, c, or s),
% and optional flags, width, and precision fields. For more
% details, type "doc fprintf" at the command prompt.
%
% * Literal text to print.
%
% * Escape characters, including:
% \b Backspace '' Single quotation mark
% \f Form feed %% Percent character
% \n New line \\ Backslash
% \r Carriage return \xN Hexadecimal number N
% \t Horizontal tab \N Octal number N
% For most cases, \n is sufficient for a single line break.
% However, if you are creating a file for use with Microsoft
% Notepad, specify a combination of \r\n to move to a new line.
%
% Notes:
%
% If you apply an integer or string conversion to a numeric value that
% contains a fraction, MATLAB overrides the specified conversion, and
% uses %e.
%
% Numeric conversions print only the real component of complex numbers.
%
% Example: Create a text file called exp.txt containing a short table of
% the exponential function.
%
% x = 0:.1:1;
% y = [x; exp(x)];
% fid = fopen('exp.txt','w');
% fprintf(fid,'%6.2f %12.8f\n',y);
% fclose(fid);
%
% Examine the contents of exp.txt:
%
% type exp.txt
%
% MATLAB returns:
% 0.00 1.00000000
% 0.10 1.10517092
% ...
% 1.00 2.71828183
%
% See also FOPEN, FCLOSE, FSCANF, FREAD, FWRITE, SPRINTF, DISP.
% Copyright 1984-2009 The MathWorks, Inc.
% Built-in function.
此函数以列为顺序将矩阵按照指定的格式转化后写入到文件，优点是占用内存小，（边转化边写入），效率高，（和第二种方法时间上差不多），推荐这种方法。
时间： 2024-08-09 23:48:01