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    1 \chapter{Data file details}
    2 \label{app-datafile}
    3 
    4 \section{Basic native format}
    5 \label{native}
    6 
    7 In gretl's basic native data format--for which we use the suffix
    8 \texttt{gdt}---a data set is stored in XML (extensible mark-up
    9 language). Data files correspond to the simple DTD (document type
   10 definition) given in \verb+gretldata.dtd+, which is supplied with the
   11 gretl distribution and is installed in the system data directory
   12 (e.g.\ \url{/usr/share/gretl/data} on Linux.)  Such files may be plain
   13 text (uncompressed) or gzipped.  They contain the actual data values
   14 plus additional information such as the names and descriptions of
   15 variables, the frequency of the data, and so on.
   16 
   17 In a \texttt{gdt} file the actual data values are written to 17
   18 significant figures (for generated data such as logs or pseudo-random
   19 numbers) or to a maximum of 15 figures for primary data. The C
   20 \texttt{printf} format ``\verb|%.*g|'' is used (for \texttt{*} = 17 or
   21 15) so that trailing zeros are not printed.
   22 
   23 Most users will probably not have need to read or write such files
   24 other than via gretl itself, but if you want to manipulate them
   25 using other software tools you should examine the DTD and also take a
   26 look at a few of the supplied practice data files: \verb+data4-1.gdt+
   27 gives a simple example; \verb+data4-10.gdt+ is an example where
   28 observation labels are included.
   29 
   30 \section{Binary data file format}
   31 \label{bindata}
   32 
   33 As of gretl 1.9.15, an alternative, binary format is available for
   34 data storage. Files of this sort have suffix \texttt{gdtb}, and they
   35 take the form of a \app{PKZIP} archive containing two files,
   36 \texttt{data.xml} and \texttt{data.bin}, with the following
   37 characteristics.
   38 \begin{itemize}
   39 \item \texttt{data.xml} is an XML file conforming to the gretldata DTD
   40   mentioned above, holding all the metadata.
   41 \item \texttt{data.bin} starts with a header composed of one of the
   42   strings
   43 
   44   \texttt{gretl-bin:little-endian} \,\,or \\
   45   \texttt{gretl-bin:big-endian}
   46 
   47   padded to 24 bytes with nul characters.  This is followed by a
   48   binary dump of the data series, by variable, as double-precision
   49   floating-point values.
   50 \end{itemize}
   51 
   52 Binary values are saved in the endianness of the machine on which
   53 they're written; the header information enables gretl to convert to
   54 the endianness of the host on which the data are read if need be.
   55 
   56 The rationale for introducing the binary \texttt{gdtb} format is that
   57 for very large datasets it is a lot faster to write and read data in
   58 this form rather than as text. For small to moderately sized datasets
   59 (say, up to 10 megabytes or so) there is no appreciable advantage in the
   60 binary format and we recommend use of plain \texttt{gdt}. 
   61 
   62 Some illustrative timings are shown in Table~\ref{tab:dataspeed};
   63 these were obtained on a Lenovo ThinkPad X1 Carbon running gretl
   64 1.9.15.  The datasets contained a mixture of random normal series and
   65 random binary (dummy) series. The largest comprised 50000 observations
   66 on 1000 series and the smallest 5000 observations on 250 series.  As
   67 can be seen, there is a big time saving from the binary format when
   68 writing (and to a lesser extent, when reading) a dataset in the
   69 hundreds of megabytes range. At a size of around 10 megabytes,
   70 however, \texttt{gdt} files can be both written and read in under a
   71 second, surely fast enough for most purposes.
   72 
   73 \begin{table}[htbp]
   74   \centering
   75   \begin{tabular}{lrr@{\hskip 2em}rr@{\hskip 2em}rr@{\hskip 2em}rr}
   76     & \multicolumn{2}{c}{381\,MB}
   77     & \multicolumn{2}{c}{38\,MB}
   78     & \multicolumn{2}{c}{19\,MB}
   79     & \multicolumn{2}{c}{10\,MB} \\
   80     format & write & read & write & read & write & read & write & read\\
   81     \texttt{gdt} & 
   82     21.76 & 4.91 & 2.20 & 0.48 & 1.19 & 0.32 & 0.59 & 0.16\\
   83     \texttt{gdtb} & 
   84     3.82 & 1.10 & 0.39 & 0.11 & 0.25 & 0.06 & 0.13 & 0.03
   85   \end{tabular}
   86   \caption{Data write and read timings in seconds for datasets
   87     of various sizes in megabytes. The MB numbers represent the 
   88     size of the datasets in memory; files of both formats are
   89     substantially smaller when compression is applied.}
   90   \label{tab:dataspeed}
   91 \end{table}
   92 
   93 
   94 \section{Native database format}
   95 \label{dbdetails}
   96 
   97 A gretl database consists of two parts: an ASCII index file (with
   98 filename suffix \texttt{.idx}) containing information on the series,
   99 and a binary file (suffix \texttt{.bin}) containing the actual data.
  100 Two examples of the format for an entry in the \texttt{idx} file are
  101 shown below:
  102 
  103 \begin{code}
  104 G0M910  Composite index of 11 leading indicators (1987=100) 
  105 M 1948.01 - 1995.11  n = 575
  106 currbal Balance of Payments: Balance on Current Account; SA 
  107 Q 1960.1 - 1999.4 n = 160
  108 \end{code}
  109 
  110 The first field is the series name.  The second is a description of
  111 the series (maximum 128 characters).  On the second line the first
  112 field is a frequency code: \texttt{M} for monthly, \texttt{Q} for
  113 quarterly, \texttt{A} for annual, \texttt{B} for business-daily (daily
  114 with five days per week), \texttt{D} for 7-day daily, \texttt{S} for
  115 6-day daily, \texttt{U} for undated.
  116 
  117 No other frequencies are accepted at present.  Then comes the starting
  118 date (N.B. with two digits following the point for monthly data, one
  119 for quarterly data, none for annual), a space, a hyphen, another
  120 space, the ending date, the string ``\verb+n = +'' and the integer
  121 number of observations. In the case of daily data the starting and
  122 ending dates should be given in the form \verb+YYYY-MM-DD+. This
  123 format must be respected exactly.
  124 
  125 Optionally, the first line of the index file may contain a short
  126 comment (up to 64 characters) on the source and nature of the data,
  127 following a hash mark.  For example:
  128 
  129 \begin{code}
  130 # Federal Reserve Board (interest rates)
  131 \end{code}
  132 
  133 The corresponding binary database file holds the data values,
  134 represented as ``floats'', that is, single-precision floating-point
  135 numbers, typically taking four bytes apiece.  The numbers are packed
  136 ``by variable'', so that the first \emph{n} numbers are the
  137 observations of variable 1, the next \emph{m} the observations on
  138 variable 2, and so on.
  139 
  140 \chapter{Building gretl}
  141 \label{app-build}
  142 
  143 Here we give instructions detailed enough to allow a user
  144 with only a basic knowledge of a Unix-type system to build gretl.
  145 These steps were tested on a fresh installation of Debian Etch. For
  146 other Linux distributions (especially Debian-based ones, like Ubuntu
  147 and its derivatives) little should change. Other Unix-like operating
  148 systems such as Mac OS X and BSD would probably require more substantial
  149 adjustments.
  150 
  151 In this guided example, we will build gretl complete with
  152 documentation.  This introduces a few more requirements, but gives you
  153 the ability to modify the documentation files as well, like the help
  154 files or the manuals.
  155 
  156 \section{Installing the prerequisites}
  157 
  158 We assume that the basic GNU utilities are already installed on the
  159 system, together with these other programs:
  160 \begin{itemize}
  161 \item some \TeX/\LaTeX system (\texttt{texlive} will do beautifully)
  162 \item Gnuplot
  163 \item ImageMagick
  164 \end{itemize}
  165 We also assume that the user has administrative privileges and knows
  166 how to install packages.  The examples below are carried out using the
  167 \texttt{apt-get} shell command, but they can be performed with
  168 menu-based utilities like \texttt{aptitude}, \texttt{dselect} or the
  169 GUI-based program \texttt{synaptic}. Users of Linux distributions
  170 which employ rpm packages (e.g.\ Red Hat/Fedora, Mandriva, SuSE) may
  171 want to refer to the
  172 \href{http://gretl.sourceforge.net/depend.html}{dependencies} page on
  173 the gretl website.
  174 
  175 The first step is installing the C compiler and related basic
  176 utilities, if these are not already in place. On a Debian (or
  177 derivative) system, these are contained in a bunch of packages that
  178 can be installed via the command
  179 \begin{code}
  180 apt-get install gcc autoconf automake1.9 libtool flex bison gcc-doc \
  181 libc6-dev libc-dev gfortran gettext pkgconfig
  182 \end{code}
  183 
  184 Then it is necessary to install the ``development'' (\texttt{dev})
  185 packages for the libraries that gretl uses: 
  186 \begin{center}
  187   \begin{tabular}{ll}
  188     \textit{Library} & \textit{command} \\ [4pt]
  189     GLIB     & \texttt{apt-get install libglib2.0-dev} \\
  190     GTK 3.0  & \texttt{apt-get install libgtk3.0-dev} \\
  191     PNG      & \texttt{apt-get install libpng12-dev} \\
  192     XSLT     & \texttt{apt-get install libxslt1-dev} \\
  193     LAPACK   & \texttt{apt-get install liblapack-dev} \\
  194     FFTW     & \texttt{apt-get install libfftw3-dev} \\
  195     READLINE & \texttt{apt-get install libreadline-dev} \\
  196     ZLIB     & \texttt{apt-get install zlib1g-dev} \\
  197     XML      & \texttt{apt-get install libxml2-dev} \\
  198     GMP      & \texttt{apt-get install libgmp-dev} \\
  199     CURL     & \texttt{apt-get install libcurl4-gnutls-dev} \\
  200     MPFR     & \texttt{apt-get install libmpfr-dev}
  201   \end{tabular}
  202 \end{center}
  203 
  204 It is possible to substitute GTK 2.0 for GTK 3.0.  The \texttt{dev}
  205 packages for these libraries are necessary to \emph{compile}
  206 gretl---you'll also need the plain, non-\texttt{dev} library packages
  207 to \emph{run} gretl, but most of these should already be part of a
  208 standard installation.  In order to enable other optional features,
  209 like audio support, you may need to install more libraries.
  210 
  211 \tip{The above steps can be much simplified on Linux systems
  212 that provide deb-based package managers, such as Debian and its
  213 derivatives (Ubuntu, Knoppix and other distributions). The command
  214 
  215 \texttt{apt-get build-dep gretl}
  216 
  217 will download and install all the necessary packages for building the
  218 version of gretl that is currently present in your APT
  219 sources. Techincally, this does not guarantee that all the software
  220 necessary to build the git version is included, because the version of
  221 gretl on your repository may be quite old and build requirements
  222 may have changed in the meantime. However, the chances of a mismatch
  223 are rather remote for a reasonably up-to-date system, so in most cases
  224 the above command should take care of everything correctly.}
  225 
  226 \section{Getting the source: release or git}
  227 
  228 At this point, it is possible to build from the source.  You have two
  229 options here: obtain the latest released source package, or retrieve
  230 the current git version of gretl (git = the version control software
  231 currently in use for gretl).  The usual caveat applies to the git
  232 version, namely, that it may not build correctly and may contain
  233 ``experimental'' code; on the other hand, git often contains bug-fixes
  234 relative to the released version.  If you want to help with testing
  235 and to contribute bug reports, we recommend using git gretl.
  236 
  237 To work with the released source:
  238 \begin{enumerate}
  239 \item Download the gretl source package from
  240   \href{http://gretl.sourceforge.net/}{gretl.sourceforge.net}.
  241 \item Unzip and untar the package.  On a system with the GNU utilities
  242   available, the command would be \cmd{tar xvfJ gretl-N.tar.xz}
  243   (replace \cmd{N} with the specific version number of the file you
  244   downloaded at step 1).
  245 \item Change directory to the gretl source directory created at step 2
  246   (e.g.\ \verb+gretl-1.10.2+).
  247 \item Proceed to the next section, ``Configure and make''.
  248 \end{enumerate}
  249 
  250 To work with git you'll first need to install the \app{git} client
  251 program if it's not already on your system.  Relevant resources you
  252 may wish to consult include the main git website at
  253 \href{https://git-scm.com/}{git-scm.com} and instructions specific to
  254 gretl:
  255 \href{http://gretl.sourceforge.net/gretl-git-basics.html}{gretl
  256   git basics}.
  257 
  258 When grabbing the git sources \textit{for the first time}, you should
  259 first decide where you want to store the code.  For example, you might
  260 create a directory called \texttt{git} under your home directory.
  261 Open a terminal window, \texttt{cd} into this directory, and type
  262 the following commands:
  263 %
  264 \begin{code}
  265 git clone git://git.code.sf.net/p/gretl/git gretl-git
  266 \end{code}
  267 %
  268 At this point \app{git} should create a subdirectory named
  269 \texttt{gretl-git} and fill it with the current sources.
  270 
  271 When you want to \textit{update the source}, this is very simple: just
  272 move into the \texttt{gretl-git} directory and type
  273 \begin{code}
  274 git pull
  275 \end{code}
  276 
  277 Assuming you're now in the \texttt{gretl-git} directory, you can
  278 proceed in the same manner as with the released source package.
  279 
  280 
  281 \section{Configure the source}
  282           
  283 The next command you need is \texttt{./configure}; this is a complex
  284 script that detects which tools you have on your system and sets
  285 things up. The \texttt{configure} command accepts many
  286 options; you may want to run 
  287 \begin{code}
  288 ./configure --help
  289 \end{code}
  290 first to see what options are available. One option you way wish to
  291 tweak is \cmd{--prefix}.  By default the installation goes under
  292 \verb+/usr/local+ but you can change this.  For example
  293 \begin{code}
  294 ./configure --prefix=/usr
  295 \end{code}
  296 will put everything under the \verb+/usr+ tree.  
  297 
  298 If you have a multi-core machine you may want to activate support
  299 for OpenMP, which permits the parallelization of matrix
  300 multiplication and some other tasks. This requires adding the
  301 \texttt{configure} flag
  302 \begin{code}
  303 --enable-openmp
  304 \end{code}
  305 
  306 By default the gretl GUI is built using version 3.0 of the GTK
  307 library, if available, otherwise version 2.0. If you have both
  308 versions installed and prefer to use GTK 2.0, use the flag
  309 \begin{code}
  310 --enable-gtk2
  311 \end{code}
  312 
  313 In order to have the documentation built, we need to pass the relevant
  314 option to \texttt{configure}, as in
  315 \begin{code}
  316 --enable-build-doc
  317 \end{code}
  318 But please note that this option will work only if you are using
  319 the git source.
  320 
  321 
  322 \tip{In order to build the documentation, there is the possibility
  323   that you will have to install some extra software on top of the
  324   packages mentioned in the previous section. For example, you may
  325   need some extra \LaTeX\ packages to compile the manuals. Two of the
  326   required packages, that not every standard \LaTeX\ installation
  327   include, are typically \app{pifont.sty} and \app{appendix.sty}. You
  328   could install the corresponding packages from your distribution or
  329   you could simply download them from CTAN and install them by hand.}
  330 
  331 
  332 This, for example, if you want to install under \texttt{/usr}, with
  333 OpenMP support, and also build the documentation, you would do
  334 \begin{code}
  335 ./configure --prefix=/usr \
  336  --enable-openmp \
  337  --enable-build-doc
  338 \end{code}
  339 
  340 You will see a number of checks being run, and if everything goes
  341 according to plan, you should see a summary similar to that displayed
  342 in Listing~\ref{configure-output}.
  343 
  344 \begin{script}[htbp]
  345   \caption{Sample output from \texttt{./configure}}
  346   \label{configure-output}
  347 \begin{scode}
  348 Configuration:
  349 
  350   Installation path:                      /usr
  351   Use readline library:                   yes
  352   Use gnuplot for graphs:                 yes
  353   Use LaTeX for typesetting output:       yes
  354   Use libgsf for zip/unzip:               no
  355   sse2 support for RNG:                   yes
  356   OpenMP support:                         yes
  357   MPI support:                            no
  358   AVX support for arithmetic:             no
  359   Build with GTK version:                 2.0
  360   Build gretl documentation:              yes
  361   Use Lucida fonts:                       no
  362   Build message catalogs:                 yes
  363   X-12-ARIMA support:                     yes
  364   TRAMO/SEATS support:                    yes
  365   libR support:                           yes
  366   ODBC support:                           no
  367   Experimental audio support:             no
  368   Use xdg-utils in installation:          if DESTDIR not set
  369   LAPACK libraries:
  370     -llapack -lblas -lgfortran
  371 
  372 Now type 'make' to build gretl.
  373 You can also do 'make pdfdocs' to build the PDF documentation.
  374 \end{scode}
  375 \end{script}
  376 
  377 \tip{If you're using git, it's a good idea to re-run the
  378   \texttt{configure} script after doing an update.  This is not always
  379   necessary, but sometimes it is, and it never does any harm.  For
  380   this purpose, you may want to write a little shell script that calls
  381   \texttt{configure} with any options you want to use.}
  382 
  383 
  384 \section{Build and install}
  385 
  386 We are now ready to undertake the compilation proper: this is done by
  387 running the \texttt{make} command, which takes care of compiling all
  388 the necessary source files in the correct order. All you need to do is
  389 type
  390 \begin{code}
  391 make 
  392 \end{code}
  393 
  394 This step will likely take several minutes to complete; a lot of
  395 output will be produced on screen. Once this is done, you can install
  396 your freshly baked copy of gretl on your system via
  397 \begin{code}
  398 make install
  399 \end{code}
  400 
  401 On most systems, the \texttt{make install} command requires you to
  402 have administrative privileges.  Hence, either you log in as
  403 \texttt{root} before launching \texttt{make install} or you may want
  404 to use the \texttt{sudo} utility, as in:
  405 \begin{code}
  406 sudo make install
  407 \end{code}
  408 
  409 Now try if everything works: go back to your home directory and run gretl
  410 \begin{code}
  411 cd ~
  412 gretl &
  413 \end{code}
  414 
  415 If all is well, you ought to see gretl start, at which point just exit
  416 the program in the usual way. On the other hand, there is the
  417 possibility that gretl doesn't start and instead you see a message
  418 like
  419 
  420 \begin{code}
  421    /usr/local/bin/gretl_x11: error while loading shared libraries:
  422    libgretl-1.0.so.0: cannot open shared object file: No such file or directory
  423 \end{code}
  424 
  425 In this case, just run
  426 \begin{code}
  427   sudo ldconfig
  428 \end{code}
  429 The problem should be fixed once and for all.
  430 
  431 \chapter{Numerical accuracy}
  432 \label{app-accuracy}
  433 
  434 Gretl uses double-precision arithmetic throughout---except for
  435 the multiple-precision plugin invoked by the menu item ``Model, Other
  436 linear models, High precision OLS'' which represents floating-point
  437 values using a number of bits given by the environment variable
  438 \verb+GRETL_MP_BITS+ (default value 256).  
  439 
  440 The normal equations of Least Squares are by default solved via
  441 Cholesky decomposition, which is highly accurate provided the matrix
  442 of cross-products of the regressors, $X'X$, is not very ill
  443 conditioned.  If this problem is detected, gretl automatically
  444 switches to use QR decomposition.
  445 
  446 The program has been tested rather thoroughly on the statistical
  447 reference datasets provided by NIST (the U.S.  National Institute of
  448 Standards and Technology) and a full account of the results may be
  449 found on the gretl website (follow the link ``Numerical accuracy'').
  450 
  451 To date, two published reviews have discussed gretl's accuracy:
  452 Giovanni Baiocchi and Walter Distaso \citeyearpar{baiocchi03}, and
  453 Talha Yalta and Yasemin Yalta \citeyearpar{yalta07}.  We are grateful
  454 to these authors for their careful examination of the program.  Their
  455 comments have prompted several modifications including the use of
  456 Stephen Moshier's \app{cephes} code for computing p-values and other
  457 quantities relating to probability distributions (see
  458 \href{http://www.netlib.org/cephes/}{netlib.org}), changes to the
  459 formatting of regression output to ensure that the program displays a
  460 consistent number of significant digits, and attention to compiler
  461 issues in producing the MS Windows version of gretl (which at
  462 one time was slighly less accurate than the Linux version).
  463 
  464 Gretl now includes a ``plugin'' that runs the NIST linear
  465 regression test suite.  You can find this under the ``Tools'' menu in
  466 the main window.  When you run this test, the introductory text
  467 explains the expected result.  If you run this test and see anything
  468 other than the expected result, please send a bug report to
  469 \verb+cottrell@wfu.edu+.
  470 
  471 All regression statistics are printed to 6 significant figures in the
  472 current version of gretl (except when the multiple-precision
  473 plugin is used, in which case results are given to 12 figures).  If
  474 you want to examine a particular value more closely, first save it
  475 (for example, using the \cmd{genr} command) then print it using
  476 \cmd{printf}, to as many digits as you like (see the \GCR).  
  477 
  478 \chapter{Related free software}
  479 \label{app-advanced}
  480 
  481 Gretl's capabilities are substantial, and are expanding.
  482 Nonetheless you may find there are some things you can't do in
  483 gretl, or you may wish to compare results with other programs.
  484 If you are looking for complementary functionality in the realm of
  485 free, open-source software we recommend the following programs.  The
  486 self-description of each program is taken from its website.
  487 
  488 \begin{itemize}
  489 
  490 \item \textbf{GNU R} \href{http://www.r-project.org/}{r-project.org}:
  491   ``R is a system for statistical computation and graphics. It
  492   consists of a language plus a run-time environment with graphics, a
  493   debugger, access to certain system functions, and the ability to run
  494   programs stored in script files\dots\ It compiles and runs on a wide
  495   variety of UNIX platforms, Windows and MacOS.''  Comment: There are
  496   numerous add-on packages for R covering most areas of statistical
  497   work.
  498 
  499 \item \textbf{GNU Octave}
  500   \href{http://www.octave.org/}{www.octave.org}:
  501   ``GNU Octave is a high-level language, primarily intended for
  502   numerical computations. It provides a convenient command line
  503   interface for solving linear and nonlinear problems numerically, and
  504   for performing other numerical experiments using a language that is
  505   mostly compatible with Matlab. It may also be used as a
  506   batch-oriented language.''
  507 
  508 \item \textbf{Julia} \href{http://julialang.org/}{julialang.org}:
  509   ``Julia is a high-level, high-performance dynamic programming
  510   language for technical computing, with syntax that is familiar to
  511   users of other technical computing environments. It provides a
  512   sophisticated compiler, distributed parallel execution, numerical
  513   accuracy, and an extensive mathematical function library.''
  514 
  515 \item \textbf{JMulTi} \href{http://www.jmulti.de/}{www.jmulti.de}:
  516   ``JMulTi was originally designed as a tool for certain econometric
  517   procedures in time series analysis that are especially difficult to
  518   use and that are not available in other packages, like Impulse
  519   Response Analysis with bootstrapped confidence intervals for VAR/VEC
  520   modelling. Now many other features have been integrated as well to
  521   make it possible to convey a comprehensive analysis.''  Comment:
  522   JMulTi is a java GUI program: you need a java run-time environment to
  523   make use of it.
  524 
  525 \end{itemize}
  526 
  527 As mentioned above, gretl offers the facility of exporting
  528 data in the formats of both Octave and R.  In the case of Octave, the
  529 gretl data set is saved as a single matrix, \verb+X+. You can
  530 pull the \verb+X+ matrix apart if you wish, once the data are loaded
  531 in Octave; see the Octave manual for details.  As for R, the exported
  532 data file preserves any time series structure that is apparent to
  533 gretl.  The series are saved as individual structures. The data
  534 should be brought into R using the \cmd{source()} command.
  535   
  536 In addition, gretl has a convenience function for moving data
  537 quickly into R.  Under gretl's ``Tools'' menu, you will find the
  538 entry ``Start GNU R''.  This writes out an R version of the current
  539 gretl data set (in the user's gretl directory), and sources it
  540 into a new R session.  The particular way R is invoked depends on the
  541 internal gretl variable \verb+Rcommand+, whose value may be set
  542 under the ``Tools, Preferences'' menu.  The default command is
  543 \cmd{RGui.exe} under MS Windows. Under X it is \cmd{xterm -e R}.
  544 Please note that at most three space-separated elements in this
  545 command string will be processed; any extra elements are ignored.
  546 
  547 \chapter{Listing of URLs}
  548 \label{app-urls}
  549 
  550 Below is a listing of the full URLs of websites mentioned in the text.
  551 
  552 \begin{description}
  553 
  554 \item[Estima (RATS)] \url{http://www.estima.com/}
  555 \item[FFTW3] \url{http://www.fftw.org/}
  556 \item[Gnome desktop homepage] \url{http://www.gnome.org/}
  557 \item[GNU Multiple Precision (GMP) library]
  558   \url{http://gmplib.org/}
  559 \item[CURL library]
  560   \url{http://curl.haxx.se/libcurl/}
  561 \item[GNU Octave homepage] \url{http://www.octave.org/}
  562 \item[GNU R homepage] \url{http://www.r-project.org/}
  563 \item[GNU R manual]
  564   \url{http://cran.r-project.org/doc/manuals/R-intro.pdf}
  565 \item[Gnuplot homepage] \url{http://www.gnuplot.info/}
  566 \item[Gnuplot manual] \url{http://ricardo.ecn.wfu.edu/gnuplot.html}
  567 \item[Gretl data page]
  568   \url{http://gretl.sourceforge.net/gretl_data.html}
  569 \item[Gretl homepage] \url{http://gretl.sourceforge.net/}
  570 \item[GTK+ homepage] \url{http://www.gtk.org/}
  571 \item[GTK+ port for win32]
  572   \url{https://wiki.gnome.org/Projects/GTK/Win32/}
  573 \item[InfoZip homepage]
  574   \url{http://www.info-zip.org/pub/infozip/zlib/}
  575 \item[JMulTi homepage] \url{http://www.jmulti.de/}
  576 \item[JRSoftware] \url{http://www.jrsoftware.org/}
  577 \item[Julia homepage] \url{http://julialang.org/}
  578 \item[Mingw (gcc for win32) homepage] \url{http://www.mingw.org/}
  579 \item[Minpack] \url{http://www.netlib.org/minpack/}
  580 \item[Penn World Table] \url{http://pwt.econ.upenn.edu/}
  581 \item[Readline homepage]
  582   \url{http://cnswww.cns.cwru.edu/~chet/readline/rltop.html}
  583 \item[Readline manual]
  584   \url{http://cnswww.cns.cwru.edu/~chet/readline/readline.html}
  585 \item[Xmlsoft homepage] \url{http://xmlsoft.org/}
  586 
  587 \end{description}
  588 
  589 
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  594