Mercurial > octave
annotate doc/interpreter/var.txi @ 19593:446c46af4b42 stable
strip trailing whitespace from most source files
* Makefile.am, NEWS, build-aux/common.mk, configure.ac,
doc/Makefile.am, doc/doxyhtml/Makefile.am,
doc/interpreter/Makefile.am, doc/interpreter/arith.txi,
doc/interpreter/audio.txi, doc/interpreter/basics.txi,
doc/interpreter/bugs.txi, doc/interpreter/container.txi,
doc/interpreter/cp-idx.txi, doc/interpreter/data.txi,
doc/interpreter/debug.txi, doc/interpreter/diagperm.txi,
doc/interpreter/diffeq.txi, doc/interpreter/doccheck/README,
doc/interpreter/doccheck/spellcheck, doc/interpreter/emacs.txi,
doc/interpreter/errors.txi, doc/interpreter/eval.txi,
doc/interpreter/expr.txi, doc/interpreter/external.txi,
doc/interpreter/fn-idx.txi, doc/interpreter/func.txi,
doc/interpreter/geometry.txi, doc/interpreter/geometryimages.m,
doc/interpreter/gpl.txi, doc/interpreter/grammar.txi,
doc/interpreter/gui.txi, doc/interpreter/image.txi,
doc/interpreter/install.txi, doc/interpreter/interp.txi,
doc/interpreter/interpimages.m, doc/interpreter/intro.txi,
doc/interpreter/io.txi, doc/interpreter/java.txi,
doc/interpreter/linalg.txi, doc/interpreter/macros.texi,
doc/interpreter/matrix.txi, doc/interpreter/munge-texi.pl,
doc/interpreter/nonlin.txi, doc/interpreter/numbers.txi,
doc/interpreter/obsolete.txi, doc/interpreter/octave-config.1,
doc/interpreter/octave.texi, doc/interpreter/oop.txi,
doc/interpreter/op-idx.txi, doc/interpreter/optim.txi,
doc/interpreter/package.txi, doc/interpreter/plot.txi,
doc/interpreter/poly.txi, doc/interpreter/preface.txi,
doc/interpreter/quad.txi, doc/interpreter/set.txi,
doc/interpreter/signal.txi, doc/interpreter/sparse.txi,
doc/interpreter/sparseimages.m, doc/interpreter/splineimages.m,
doc/interpreter/stats.txi, doc/interpreter/stmt.txi,
doc/interpreter/strings.txi, doc/interpreter/system.txi,
doc/interpreter/testfun.txi, doc/interpreter/tips.txi,
doc/interpreter/var.txi, doc/interpreter/vectorize.txi,
doc/liboctave/Makefile.am, doc/liboctave/array.texi,
doc/liboctave/bugs.texi, doc/liboctave/cp-idx.texi,
doc/liboctave/dae.texi, doc/liboctave/diffeq.texi,
doc/liboctave/error.texi, doc/liboctave/factor.texi,
doc/liboctave/fn-idx.texi, doc/liboctave/gpl.texi,
doc/liboctave/install.texi, doc/liboctave/intro.texi,
doc/liboctave/liboctave.texi, doc/liboctave/matvec.texi,
doc/liboctave/nleqn.texi, doc/liboctave/nlfunc.texi,
doc/liboctave/ode.texi, doc/liboctave/optim.texi,
doc/liboctave/preface.texi, doc/liboctave/quad.texi,
doc/liboctave/range.texi, doc/refcard/Makefile.am,
doc/refcard/refcard.tex, etc/HACKING, etc/NEWS.1, etc/NEWS.2,
etc/NEWS.3, etc/OLD-ChangeLogs/ChangeLog,
etc/OLD-ChangeLogs/doc-ChangeLog,
etc/OLD-ChangeLogs/scripts-ChangeLog,
etc/OLD-ChangeLogs/src-ChangeLog, etc/OLD-ChangeLogs/test-ChangeLog,
etc/PROJECTS, etc/README.Cygwin, etc/README.MacOS, etc/README.MinGW,
etc/README.gnuplot, etc/gdbinit, etc/icons/Makefile.am,
examples/@polynomial/end.m, examples/@polynomial/subsasgn.m,
examples/Makefile.am, examples/standalonebuiltin.cc,
libgui/Makefile.am, libgui/qterminal/libqterminal/README,
libgui/qterminal/libqterminal/unix/BlockArray.cpp,
libgui/qterminal/libqterminal/unix/BlockArray.h,
libgui/qterminal/libqterminal/unix/Character.h,
libgui/qterminal/libqterminal/unix/CharacterColor.h,
libgui/qterminal/libqterminal/unix/Emulation.cpp,
libgui/qterminal/libqterminal/unix/Emulation.h,
libgui/qterminal/libqterminal/unix/Filter.cpp,
libgui/qterminal/libqterminal/unix/Filter.h,
libgui/qterminal/libqterminal/unix/History.cpp,
libgui/qterminal/libqterminal/unix/History.h,
libgui/qterminal/libqterminal/unix/KeyboardTranslator.cpp,
libgui/qterminal/libqterminal/unix/KeyboardTranslator.h,
libgui/qterminal/libqterminal/unix/LineFont.h,
libgui/qterminal/libqterminal/unix/QUnixTerminalImpl.cpp,
libgui/qterminal/libqterminal/unix/QUnixTerminalImpl.h,
libgui/qterminal/libqterminal/unix/Screen.cpp,
libgui/qterminal/libqterminal/unix/Screen.h,
libgui/qterminal/libqterminal/unix/ScreenWindow.cpp,
libgui/qterminal/libqterminal/unix/ScreenWindow.h,
libgui/qterminal/libqterminal/unix/TerminalCharacterDecoder.cpp,
libgui/qterminal/libqterminal/unix/TerminalCharacterDecoder.h,
libgui/qterminal/libqterminal/unix/Vt102Emulation.h,
libgui/qterminal/libqterminal/win32/QWinTerminalImpl.cpp,
libgui/qterminal/qterminal/main.cpp,
libgui/src/m-editor/file-editor-tab.cc, libgui/src/octave-gui.cc,
libgui/src/octave-qt-link.cc, libinterp/corefcn/data.cc,
libinterp/corefcn/defun-int.h, libinterp/corefcn/det.cc,
libinterp/corefcn/gl2ps-renderer.cc, libinterp/corefcn/graphics.cc,
libinterp/corefcn/graphics.in.h, libinterp/corefcn/ls-mat5.cc,
libinterp/corefcn/lu.cc, libinterp/corefcn/oct-tex-parser.yy,
libinterp/corefcn/oct-tex-symbols.in, libinterp/corefcn/quadcc.cc,
libinterp/corefcn/zfstream.cc, libinterp/dldfcn/__eigs__.cc,
libinterp/dldfcn/__voronoi__.cc, libinterp/gendoc.pl,
libinterp/genprops.awk, libinterp/mk-errno-list, libinterp/mk-pkg-add,
libinterp/mkbuiltins, libinterp/mkdefs, libinterp/mkdocs,
libinterp/mkops, libinterp/octave-value/ov-java.cc,
libinterp/parse-tree/lex.ll, libinterp/parse-tree/oct-parse.in.yy,
libinterp/parse-tree/octave.gperf, liboctave/Makefile.am,
liboctave/array/Array.cc, liboctave/array/module.mk,
liboctave/cruft/daspk/datv.f, liboctave/cruft/daspk/dcnst0.f,
liboctave/cruft/daspk/dcnstr.f, liboctave/cruft/daspk/ddasic.f,
liboctave/cruft/daspk/ddasid.f, liboctave/cruft/daspk/ddasik.f,
liboctave/cruft/daspk/ddaspk.f, liboctave/cruft/daspk/ddstp.f,
liboctave/cruft/daspk/ddwnrm.f, liboctave/cruft/daspk/dfnrmd.f,
liboctave/cruft/daspk/dfnrmk.f, liboctave/cruft/daspk/dhels.f,
liboctave/cruft/daspk/dheqr.f, liboctave/cruft/daspk/dinvwt.f,
liboctave/cruft/daspk/dlinsd.f, liboctave/cruft/daspk/dlinsk.f,
liboctave/cruft/daspk/dmatd.f, liboctave/cruft/daspk/dnedd.f,
liboctave/cruft/daspk/dnedk.f, liboctave/cruft/daspk/dnsd.f,
liboctave/cruft/daspk/dnsid.f, liboctave/cruft/daspk/dnsik.f,
liboctave/cruft/daspk/dnsk.f, liboctave/cruft/daspk/dorth.f,
liboctave/cruft/daspk/dslvd.f, liboctave/cruft/daspk/dslvk.f,
liboctave/cruft/daspk/dspigm.f, liboctave/cruft/daspk/dyypnw.f,
liboctave/cruft/dasrt/ddasrt.f, liboctave/cruft/dasrt/drchek.f,
liboctave/cruft/dassl/ddaslv.f, liboctave/cruft/dassl/ddassl.f,
liboctave/cruft/misc/blaswrap.c, liboctave/cruft/misc/module.mk,
liboctave/cruft/odepack/cfode.f, liboctave/cruft/odepack/dlsode.f,
liboctave/cruft/odepack/ewset.f, liboctave/cruft/odepack/intdy.f,
liboctave/cruft/odepack/prepj.f, liboctave/cruft/odepack/sintdy.f,
liboctave/cruft/odepack/slsode.f, liboctave/cruft/odepack/solsy.f,
liboctave/cruft/odepack/ssolsy.f, liboctave/cruft/odepack/stode.f,
liboctave/cruft/odepack/vnorm.f, liboctave/cruft/ranlib/Basegen.doc,
liboctave/cruft/ranlib/README, liboctave/cruft/ranlib/genbet.f,
liboctave/cruft/ranlib/genexp.f, liboctave/cruft/ranlib/gennch.f,
liboctave/cruft/ranlib/gennf.f, liboctave/cruft/ranlib/gennor.f,
liboctave/cruft/ranlib/getsd.f, liboctave/cruft/ranlib/initgn.f,
liboctave/cruft/ranlib/phrtsd.f, liboctave/cruft/ranlib/randlib.fdoc,
liboctave/cruft/ranlib/setsd.f, liboctave/cruft/ranlib/tstgmn.for,
liboctave/cruft/ranlib/tstmid.for, liboctave/cruft/slatec-fn/atanh.f,
liboctave/cruft/slatec-fn/datanh.f,
liboctave/cruft/slatec-fn/xgmainc.f,
liboctave/cruft/slatec-fn/xsgmainc.f, liboctave/numeric/module.mk,
liboctave/operators/mk-ops.awk, liboctave/operators/mx-ops,
liboctave/operators/sparse-mk-ops.awk,
liboctave/operators/sparse-mx-ops, liboctave/operators/vx-ops,
liboctave/util/module.mk, run-octave.in, scripts/@ftp/ftp.m,
scripts/audio/wavread.m, scripts/deprecated/java_convert_matrix.m,
scripts/deprecated/java_debug.m, scripts/deprecated/java_invoke.m,
scripts/deprecated/java_new.m,
scripts/deprecated/java_unsigned_conversion.m,
scripts/deprecated/javafields.m, scripts/deprecated/javamethods.m,
scripts/deprecated/shell_cmd.m, scripts/general/accumarray.m,
scripts/general/display.m, scripts/general/fieldnames.m,
scripts/general/interp1.m, scripts/general/interp2.m,
scripts/general/interp3.m, scripts/general/isa.m,
scripts/general/methods.m, scripts/general/sortrows.m,
scripts/geometry/convhull.m, scripts/geometry/delaunay.m,
scripts/geometry/delaunay3.m, scripts/geometry/delaunayn.m,
scripts/geometry/griddata.m, scripts/geometry/griddatan.m,
scripts/geometry/voronoi.m, scripts/geometry/voronoin.m,
scripts/gui/guihandles.m, scripts/gui/inputdlg.m,
scripts/gui/listdlg.m, scripts/gui/msgbox.m, scripts/gui/questdlg.m,
scripts/gui/uigetfile.m, scripts/gui/waitbar.m, scripts/gui/warndlg.m,
scripts/help/doc.m, scripts/help/help.m, scripts/help/type.m,
scripts/image/bone.m, scripts/image/cmpermute.m,
scripts/image/cmunique.m, scripts/image/colorcube.m,
scripts/image/colormap.m, scripts/image/contrast.m,
scripts/image/gray2ind.m, scripts/image/image.m,
scripts/image/imshow.m, scripts/image/ind2gray.m, scripts/image/jet.m,
scripts/image/rgb2ntsc.m, scripts/image/spinmap.m,
scripts/io/importdata.m, scripts/io/strread.m, scripts/io/textread.m,
scripts/io/textscan.m, scripts/java/java_get.m,
scripts/java/java_set.m, scripts/java/javaaddpath.m,
scripts/java/javaclasspath.m, scripts/java/javamem.m,
scripts/linear-algebra/linsolve.m, scripts/linear-algebra/qzhess.m,
scripts/miscellaneous/debug.m, scripts/miscellaneous/desktop.m,
scripts/miscellaneous/dir.m, scripts/miscellaneous/dos.m,
scripts/miscellaneous/edit.m, scripts/miscellaneous/fact.m,
scripts/miscellaneous/getappdata.m, scripts/miscellaneous/inputname.m,
scripts/miscellaneous/license.m, scripts/miscellaneous/ls_command.m,
scripts/miscellaneous/run.m, scripts/miscellaneous/setfield.m,
scripts/miscellaneous/unix.m, scripts/miscellaneous/ver.m,
scripts/mk-pkg-add, scripts/mkdoc.pl,
scripts/optimization/fminsearch.m, scripts/optimization/optimset.m,
scripts/optimization/sqp.m, scripts/pkg/pkg.m,
scripts/pkg/private/create_pkgadddel.m,
scripts/pkg/private/fix_depends.m, scripts/pkg/private/install.m,
scripts/plot/appearance/axis.m, scripts/plot/appearance/box.m,
scripts/plot/appearance/clabel.m, scripts/plot/appearance/daspect.m,
scripts/plot/appearance/datetick.m, scripts/plot/appearance/grid.m,
scripts/plot/appearance/legend.m, scripts/plot/appearance/orient.m,
scripts/plot/appearance/shading.m, scripts/plot/appearance/text.m,
scripts/plot/appearance/title.m, scripts/plot/appearance/xlabel.m,
scripts/plot/appearance/ylabel.m, scripts/plot/appearance/zlabel.m,
scripts/plot/draw/area.m, scripts/plot/draw/bar.m,
scripts/plot/draw/barh.m, scripts/plot/draw/colorbar.m,
scripts/plot/draw/contour.m, scripts/plot/draw/contour3.m,
scripts/plot/draw/contourf.m, scripts/plot/draw/ellipsoid.m,
scripts/plot/draw/errorbar.m, scripts/plot/draw/ezcontour.m,
scripts/plot/draw/ezcontourf.m, scripts/plot/draw/ezmesh.m,
scripts/plot/draw/ezpolar.m, scripts/plot/draw/fill.m,
scripts/plot/draw/fplot.m, scripts/plot/draw/hist.m,
scripts/plot/draw/meshc.m, scripts/plot/draw/meshz.m,
scripts/plot/draw/pareto.m, scripts/plot/draw/patch.m,
scripts/plot/draw/peaks.m, scripts/plot/draw/pie.m,
scripts/plot/draw/pie3.m, scripts/plot/draw/plot.m,
scripts/plot/draw/plotyy.m, scripts/plot/draw/private/__bar__.m,
scripts/plot/draw/private/__contour__.m,
scripts/plot/draw/private/__errplot__.m,
scripts/plot/draw/private/__ezplot__.m,
scripts/plot/draw/private/__patch__.m,
scripts/plot/draw/private/__stem__.m, scripts/plot/draw/rectangle.m,
scripts/plot/draw/ribbon.m, scripts/plot/draw/rose.m,
scripts/plot/draw/scatter.m, scripts/plot/draw/scatter3.m,
scripts/plot/draw/semilogx.m, scripts/plot/draw/shrinkfaces.m,
scripts/plot/draw/sombrero.m, scripts/plot/draw/sphere.m,
scripts/plot/draw/stairs.m, scripts/plot/draw/stem.m,
scripts/plot/draw/stemleaf.m, scripts/plot/draw/surf.m,
scripts/plot/draw/surface.m, scripts/plot/draw/surfc.m,
scripts/plot/draw/surfl.m, scripts/plot/draw/surfnorm.m,
scripts/plot/draw/tetramesh.m, scripts/plot/draw/trimesh.m,
scripts/plot/draw/triplot.m, scripts/plot/draw/trisurf.m,
scripts/plot/util/__gnuplot_drawnow__.m,
scripts/plot/util/__plt_get_axis_arg__.m, scripts/plot/util/axes.m,
scripts/plot/util/clf.m, scripts/plot/util/copyobj.m,
scripts/plot/util/figure.m, scripts/plot/util/gcbo.m,
scripts/plot/util/graphics_toolkit.m, scripts/plot/util/hggroup.m,
scripts/plot/util/meshgrid.m, scripts/plot/util/newplot.m,
scripts/plot/util/print.m,
scripts/plot/util/private/__add_default_menu__.m,
scripts/plot/util/private/__fltk_print__.m,
scripts/plot/util/private/__gnuplot_print__.m,
scripts/plot/util/private/__print_parse_opts__.m,
scripts/plot/util/refreshdata.m, scripts/plot/util/subplot.m,
scripts/polynomial/conv.m, scripts/polynomial/poly.m,
scripts/polynomial/polyeig.m, scripts/polynomial/polyfit.m,
scripts/polynomial/polyval.m,
scripts/polynomial/private/__splinefit__.m,
scripts/polynomial/spline.m, scripts/prefs/prefdir.m,
scripts/prefs/preferences.m, scripts/prefs/private/prefsfile.m,
scripts/prefs/rmpref.m, scripts/signal/freqz.m,
scripts/signal/module.mk, scripts/sparse/eigs.m, scripts/sparse/pcg.m,
scripts/sparse/private/__sprand_impl__.m, scripts/sparse/sprand.m,
scripts/sparse/sprandn.m, scripts/sparse/spy.m, scripts/sparse/svds.m,
scripts/specfun/expint.m, scripts/specfun/factor.m,
scripts/special-matrix/gallery.m, scripts/special-matrix/hankel.m,
scripts/special-matrix/toeplitz.m, scripts/startup/inputrc,
scripts/statistics/base/kurtosis.m, scripts/statistics/base/moment.m,
scripts/statistics/base/qqplot.m, scripts/statistics/base/var.m,
scripts/statistics/distributions/betarnd.m,
scripts/statistics/distributions/binoinv.m,
scripts/statistics/distributions/binopdf.m,
scripts/statistics/distributions/binornd.m,
scripts/statistics/distributions/cauchy_rnd.m,
scripts/statistics/distributions/chi2rnd.m,
scripts/statistics/distributions/discrete_pdf.m,
scripts/statistics/distributions/discrete_rnd.m,
scripts/statistics/distributions/empirical_rnd.m,
scripts/statistics/distributions/exprnd.m,
scripts/statistics/distributions/frnd.m,
scripts/statistics/distributions/gamrnd.m,
scripts/statistics/distributions/geornd.m,
scripts/statistics/distributions/hygernd.m,
scripts/statistics/distributions/kolmogorov_smirnov_cdf.m,
scripts/statistics/distributions/laplace_cdf.m,
scripts/statistics/distributions/laplace_pdf.m,
scripts/statistics/distributions/logistic_cdf.m,
scripts/statistics/distributions/logistic_pdf.m,
scripts/statistics/distributions/lognrnd.m,
scripts/statistics/distributions/nbincdf.m,
scripts/statistics/distributions/nbininv.m,
scripts/statistics/distributions/nbinpdf.m,
scripts/statistics/distributions/nbinrnd.m,
scripts/statistics/distributions/normrnd.m,
scripts/statistics/distributions/poissinv.m,
scripts/statistics/distributions/poissrnd.m,
scripts/statistics/distributions/tinv.m,
scripts/statistics/distributions/trnd.m,
scripts/statistics/distributions/unidcdf.m,
scripts/statistics/distributions/unidpdf.m,
scripts/statistics/distributions/unidrnd.m,
scripts/statistics/distributions/unifrnd.m,
scripts/statistics/distributions/wblrnd.m,
scripts/statistics/models/module.mk,
scripts/statistics/tests/kruskal_wallis_test.m,
scripts/strings/base2dec.m, scripts/strings/deblank.m,
scripts/strings/dec2base.m, scripts/strings/dec2bin.m,
scripts/strings/dec2hex.m, scripts/strings/mat2str.m,
scripts/strings/ostrsplit.m, scripts/strings/regexptranslate.m,
scripts/strings/str2num.m, scripts/strings/strcat.m,
scripts/strings/strjoin.m, scripts/strings/strsplit.m,
scripts/strings/strtok.m, scripts/strings/strtrim.m,
scripts/strings/strtrunc.m, scripts/strings/substr.m,
scripts/testfun/__run_test_suite__.m, scripts/testfun/speed.m,
scripts/testfun/test.m, scripts/time/asctime.m,
scripts/time/datenum.m, scripts/time/datevec.m,
scripts/time/weekday.m, src/Makefile.am, test/Makefile.am,
test/build-bc-overload-tests.sh, test/build-sparse-tests.sh,
test/jit.tst, test/line-continue.tst: Strip trailing whitespace.
author | John W. Eaton <jwe@octave.org> |
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date | Tue, 20 Jan 2015 08:26:57 -0500 |
parents | d63878346099 |
children | fe689210525c |
rev | line source |
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1 @c Copyright (C) 1996-2013 John W. Eaton |
7018 | 2 @c |
3 @c This file is part of Octave. | |
4 @c | |
5 @c Octave is free software; you can redistribute it and/or modify it | |
6 @c under the terms of the GNU General Public License as published by the | |
7 @c Free Software Foundation; either version 3 of the License, or (at | |
8 @c your option) any later version. | |
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9 @c |
7018 | 10 @c Octave is distributed in the hope that it will be useful, but WITHOUT |
11 @c ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
12 @c FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
13 @c for more details. | |
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14 @c |
7018 | 15 @c You should have received a copy of the GNU General Public License |
16 @c along with Octave; see the file COPYING. If not, see | |
17 @c <http://www.gnu.org/licenses/>. | |
3294 | 18 |
4167 | 19 @node Variables |
3294 | 20 @chapter Variables |
21 @cindex variables, user-defined | |
22 @cindex user-defined variables | |
23 | |
24 Variables let you give names to values and refer to them later. You have | |
25 already seen variables in many of the examples. The name of a variable | |
26 must be a sequence of letters, digits and underscores, but it may not begin | |
27 with a digit. Octave does not enforce a limit on the length of variable | |
28 names, but it is seldom useful to have variables with names longer than | |
29 about 30 characters. The following are all valid variable names | |
30 | |
31 @example | |
32 @group | |
33 x | |
34 x15 | |
35 __foo_bar_baz__ | |
36 fucnrdthsucngtagdjb | |
37 @end group | |
38 @end example | |
39 | |
40 @noindent | |
41 However, names like @code{__foo_bar_baz__} that begin and end with two | |
42 underscores are understood to be reserved for internal use by Octave. | |
43 You should not use them in code you write, except to access Octave's | |
44 documented internal variables and built-in symbolic constants. | |
45 | |
46 Case is significant in variable names. The symbols @code{a} and | |
47 @code{A} are distinct variables. | |
48 | |
49 A variable name is a valid expression by itself. It represents the | |
50 variable's current value. Variables are given new values with | |
51 @dfn{assignment operators} and @dfn{increment operators}. | |
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52 @xref{Assignment Ops,,Assignment Expressions}. |
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54 There is one built-in variable with a special meaning. The @code{ans} variable |
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55 always contains the result of the last computation, where the output wasn't |
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56 assigned to any variable. The code @code{a = cos (pi)} will assign the value -1 |
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57 to the variable @code{a}, but will not change the value of @code{ans}. However, |
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58 the code @code{cos (pi)} will set the value of @code{ans} to -1. |
3294 | 59 |
60 Variables in Octave do not have fixed types, so it is possible to first | |
61 store a numeric value in a variable and then to later use the same name | |
62 to hold a string value in the same program. Variables may not be used | |
63 before they have been given a value. Doing so results in an error. | |
64 | |
8567 | 65 @cindex @code{ans} |
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66 @DOCSTRING(ans) |
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67 |
6550 | 68 @DOCSTRING(isvarname) |
69 | |
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70 @DOCSTRING(genvarname) |
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71 |
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72 @DOCSTRING(namelengthmax) |
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73 |
3294 | 74 @menu |
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75 * Global Variables:: |
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76 * Persistent Variables:: |
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77 * Status of Variables:: |
3294 | 78 @end menu |
79 | |
4167 | 80 @node Global Variables |
3294 | 81 @section Global Variables |
82 @cindex global variables | |
83 @cindex @code{global} statement | |
84 @cindex variables, global | |
85 | |
86 A variable that has been declared @dfn{global} may be accessed from | |
87 within a function body without having to pass it as a formal parameter. | |
88 | |
89 A variable may be declared global using a @code{global} declaration | |
90 statement. The following statements are all global declarations. | |
91 | |
92 @example | |
93 @group | |
94 global a | |
4504 | 95 global a b |
96 global c = 2 | |
97 global d = 3 e f = 5 | |
3294 | 98 @end group |
99 @end example | |
100 | |
4504 | 101 A global variable may only be initialized once in a @code{global} |
102 statement. For example, after executing the following code | |
103 | |
104 @example | |
105 @group | |
106 global gvar = 1 | |
107 global gvar = 2 | |
108 @end group | |
109 @end example | |
110 | |
111 @noindent | |
6077 | 112 the value of the global variable @code{gvar} is 1, not 2. Issuing a |
6623 | 113 @samp{clear gvar} command does not change the above behavior, but |
6077 | 114 @samp{clear all} does. |
4504 | 115 |
3294 | 116 It is necessary declare a variable as global within a function body in |
117 order to access it. For example, | |
118 | |
119 @example | |
120 @group | |
121 global x | |
122 function f () | |
123 x = 1; | |
124 endfunction | |
125 f () | |
126 @end group | |
127 @end example | |
128 | |
129 @noindent | |
130 does @emph{not} set the value of the global variable @code{x} to 1. In | |
131 order to change the value of the global variable @code{x}, you must also | |
132 declare it to be global within the function body, like this | |
133 | |
134 @example | |
135 @group | |
136 function f () | |
137 global x; | |
138 x = 1; | |
139 endfunction | |
140 @end group | |
141 @end example | |
142 | |
143 Passing a global variable in a function parameter list will | |
144 make a local copy and not modify the global value. For example, given | |
145 the function | |
146 | |
147 @example | |
148 @group | |
149 function f (x) | |
150 x = 0 | |
151 endfunction | |
152 @end group | |
153 @end example | |
154 | |
155 @noindent | |
156 and the definition of @code{x} as a global variable at the top level, | |
157 | |
158 @example | |
159 global x = 13 | |
160 @end example | |
161 | |
162 @noindent | |
163 the expression | |
164 | |
165 @example | |
166 f (x) | |
167 @end example | |
168 | |
169 @noindent | |
170 will display the value of @code{x} from inside the function as 0, | |
171 but the value of @code{x} at the top level remains unchanged, because | |
172 the function works with a @emph{copy} of its argument. | |
173 | |
4029 | 174 @DOCSTRING(isglobal) |
3294 | 175 |
4686 | 176 @node Persistent Variables |
177 @section Persistent Variables | |
178 @cindex persistent variables | |
179 @cindex @code{persistent} statement | |
180 @cindex variables, persistent | |
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181 @anchor{XREFpersistent} |
4686 | 182 |
183 A variable that has been declared @dfn{persistent} within a function | |
184 will retain its contents in memory between subsequent calls to the | |
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185 same function. The difference between persistent variables and global |
4686 | 186 variables is that persistent variables are local in scope to a |
187 particular function and are not visible elsewhere. | |
188 | |
6899 | 189 The following example uses a persistent variable to create a function |
190 that prints the number of times it has been called. | |
191 | |
192 @example | |
193 @group | |
194 function count_calls () | |
195 persistent calls = 0; | |
7031 | 196 printf ("'count_calls' has been called %d times\n", |
197 ++calls); | |
6899 | 198 endfunction |
199 | |
200 for i = 1:3 | |
201 count_calls (); | |
202 endfor | |
203 | |
204 @print{} 'count_calls' has been called 1 times | |
205 @print{} 'count_calls' has been called 2 times | |
206 @print{} 'count_calls' has been called 3 times | |
207 @end group | |
208 @end example | |
209 | |
210 As the example shows, a variable may be declared persistent using a | |
211 @code{persistent} declaration statement. The following statements are | |
212 all persistent declarations. | |
4686 | 213 |
214 @example | |
215 @group | |
216 persistent a | |
217 persistent a b | |
218 persistent c = 2 | |
219 persistent d = 3 e f = 5 | |
220 @end group | |
221 @end example | |
222 | |
223 The behavior of persistent variables is equivalent to the behavior of | |
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224 static variables in C@. The command @code{static} in Octave is also |
6899 | 225 recognized and is equivalent to @code{persistent}. |
226 | |
227 Like global variables, a persistent variable may only be initialized once. | |
6896 | 228 For example, after executing the following code |
4686 | 229 |
230 @example | |
231 @group | |
232 persistent pvar = 1 | |
233 persistent pvar = 2 | |
234 @end group | |
235 @end example | |
236 | |
237 @noindent | |
6896 | 238 the value of the persistent variable @code{pvar} is 1, not 2. |
4686 | 239 |
6899 | 240 If a persistent variable is declared but not initialized to a specific |
241 value, it will contain an empty matrix. So, it is also possible to | |
242 initialize a persistent variable by checking whether it is empty, as the | |
243 following example illustrates. | |
244 | |
245 @example | |
246 @group | |
247 function count_calls () | |
248 persistent calls; | |
249 if (isempty (calls)) | |
250 calls = 0; | |
251 endif | |
7031 | 252 printf ("'count_calls' has been called %d times\n", |
253 ++calls); | |
6899 | 254 endfunction |
255 @end group | |
256 @end example | |
257 | |
258 @noindent | |
259 This implementation behaves in exactly the same way as the previous | |
260 implementation of @code{count_calls}. | |
261 | |
262 The value of a persistent variable is kept in memory until it is | |
263 explicitly cleared. Assuming that the implementation of @code{count_calls} | |
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264 is saved on disk, we get the following behavior. |
6899 | 265 |
266 @example | |
267 for i = 1:2 | |
268 count_calls (); | |
269 endfor | |
270 @print{} 'count_calls' has been called 1 times | |
271 @print{} 'count_calls' has been called 2 times | |
272 | |
273 clear | |
274 for i = 1:2 | |
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275 count_calls (); |
6899 | 276 endfor |
277 @print{} 'count_calls' has been called 3 times | |
278 @print{} 'count_calls' has been called 4 times | |
279 | |
280 clear all | |
281 for i = 1:2 | |
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282 count_calls (); |
6899 | 283 endfor |
284 @print{} 'count_calls' has been called 1 times | |
285 @print{} 'count_calls' has been called 2 times | |
286 | |
287 clear count_calls | |
288 for i = 1:2 | |
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289 count_calls (); |
6899 | 290 endfor |
291 @print{} 'count_calls' has been called 1 times | |
292 @print{} 'count_calls' has been called 2 times | |
293 @end example | |
294 | |
295 @noindent | |
296 That is, the persistent variable is only removed from memory when the | |
297 function containing the variable is removed. Note that if the function | |
298 definition is typed directly into the Octave prompt, the persistent | |
299 variable will be cleared by a simple @code{clear} command as the entire | |
300 function definition will be removed from memory. If you do not want | |
301 a persistent variable to be removed from memory even if the function is | |
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302 cleared, you should use the @code{mlock} function |
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303 (@pxref{Function Locking}). |
6899 | 304 |
4167 | 305 @node Status of Variables |
3294 | 306 @section Status of Variables |
307 | |
6623 | 308 When creating simple one-shot programs it can be very convenient to |
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309 see which variables are available at the prompt. The function @code{who} |
6623 | 310 and its siblings @code{whos} and @code{whos_line_format} will show |
311 different information about what is in memory, as the following shows. | |
312 | |
313 @example | |
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314 @group |
6623 | 315 str = "A random string"; |
316 who -variables | |
317 @print{} *** local user variables: | |
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318 @print{} |
6623 | 319 @print{} __nargin__ str |
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320 @end group |
6623 | 321 @end example |
3294 | 322 |
3361 | 323 @DOCSTRING(who) |
3294 | 324 |
4913 | 325 @DOCSTRING(whos) |
326 | |
327 @DOCSTRING(whos_line_format) | |
328 | |
6623 | 329 Instead of displaying which variables are in memory, it is possible |
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330 to determine if a given variable is available. That way it is possible |
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331 to alter the behavior of a program depending on the existence of a |
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332 variable. The following example illustrates this. |
6623 | 333 |
334 @example | |
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335 @group |
6623 | 336 if (! exist ("meaning", "var")) |
337 disp ("The program has no 'meaning'"); | |
338 endif | |
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339 @end group |
6623 | 340 @end example |
341 | |
3361 | 342 @DOCSTRING(exist) |
3294 | 343 |
6623 | 344 Usually Octave will manage the memory, but sometimes it can be practical |
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345 to remove variables from memory manually. This is usually needed when |
6623 | 346 working with large variables that fill a substantial part of the memory. |
347 On a computer that uses the IEEE floating point format, the following | |
348 program allocates a matrix that requires around 128 MB memory. | |
349 | |
350 @example | |
351 large_matrix = zeros (4000, 4000); | |
352 @end example | |
353 | |
354 @noindent | |
355 Since having this variable in memory might slow down other computations, | |
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356 it can be necessary to remove it manually from memory. The @code{clear} |
6623 | 357 function allows this. |
358 | |
359 @DOCSTRING(clear) | |
360 | |
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361 @DOCSTRING(pack) |
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362 |
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363 Information about a function or variable such as its location in the |
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364 file system can also be acquired from within Octave. This is usually |
6623 | 365 only useful during development of programs, and not within a program. |
366 | |
3361 | 367 @DOCSTRING(type) |
3294 | 368 |
3361 | 369 @DOCSTRING(which) |
3294 | 370 |
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371 @DOCSTRING(what) |