Mercurial > octave-nkf
annotate doc/interpreter/eval.txi @ 17281:bc924baa2c4e
doc: Add new @qcode macro for code samples which are quoted.
Macro handles options ("on") or properties ("position") more elegantly
than @code{"text"}.
* doc/interpreter/macros.texi: Add new @qcode macro.
* doc/interpreter/tips.txi: Add documentation about @qcode macro.
* doc/interpreter/basics.txi, doc/interpreter/container.txi,
doc/interpreter/emacs.txi, doc/interpreter/errors.txi,
doc/interpreter/eval.txi, doc/interpreter/expr.txi,
doc/interpreter/external.txi, doc/interpreter/func.txi,
doc/interpreter/grammar.txi, doc/interpreter/image.txi,
doc/interpreter/install.txi, doc/interpreter/interp.txi,
doc/interpreter/io.txi, doc/interpreter/matrix.txi,
doc/interpreter/numbers.txi, doc/interpreter/oop.txi,
doc/interpreter/package.txi, doc/interpreter/plot.txi,
doc/interpreter/quad.txi, doc/interpreter/sparse.txi,
doc/interpreter/strings.txi, doc/interpreter/system.txi,
doc/interpreter/vectorize.txi, libinterp/corefcn/balance.cc,
libinterp/corefcn/bitfcns.cc, libinterp/corefcn/cellfun.cc,
libinterp/corefcn/conv2.cc, libinterp/corefcn/data.cc,
libinterp/corefcn/debug.cc, libinterp/corefcn/defaults.cc,
libinterp/corefcn/dirfns.cc, libinterp/corefcn/dlmread.cc,
libinterp/corefcn/error.cc, libinterp/corefcn/file-io.cc,
libinterp/corefcn/find.cc, libinterp/corefcn/gammainc.cc,
libinterp/corefcn/graphics.cc, libinterp/corefcn/help.cc,
libinterp/corefcn/hex2num.cc, libinterp/corefcn/input.cc,
libinterp/corefcn/load-path.cc, libinterp/corefcn/load-save.cc,
libinterp/corefcn/ls-oct-ascii.cc, libinterp/corefcn/lu.cc,
libinterp/corefcn/luinc.cc, libinterp/corefcn/matrix_type.cc,
libinterp/corefcn/oct-hist.cc, libinterp/corefcn/pager.cc,
libinterp/corefcn/pr-output.cc, libinterp/corefcn/pt-jit.cc,
libinterp/corefcn/qz.cc, libinterp/corefcn/rand.cc,
libinterp/corefcn/regexp.cc, libinterp/corefcn/schur.cc,
libinterp/corefcn/sighandlers.cc, libinterp/corefcn/sparse.cc,
libinterp/corefcn/spparms.cc, libinterp/corefcn/str2double.cc,
libinterp/corefcn/svd.cc, libinterp/corefcn/symtab.cc,
libinterp/corefcn/syscalls.cc, libinterp/corefcn/toplev.cc,
libinterp/corefcn/tril.cc, libinterp/corefcn/typecast.cc,
libinterp/corefcn/utils.cc, libinterp/corefcn/variables.cc,
libinterp/dldfcn/__init_fltk__.cc, libinterp/dldfcn/chol.cc,
libinterp/dldfcn/colamd.cc, libinterp/dldfcn/fftw.cc, libinterp/dldfcn/qr.cc,
libinterp/dldfcn/symbfact.cc, libinterp/octave-value/ov-base.cc,
libinterp/octave-value/ov-fcn-handle.cc,
libinterp/octave-value/ov-fcn-inline.cc, libinterp/octave-value/ov-java.cc,
libinterp/octave-value/ov-range.cc, libinterp/octave-value/ov-struct.cc,
libinterp/octave-value/ov-usr-fcn.cc, libinterp/parse-tree/oct-parse.in.yy,
libinterp/parse-tree/pt-binop.cc, libinterp/parse-tree/pt-eval.cc,
libinterp/parse-tree/pt-mat.cc, scripts/@ftp/ftp.m,
scripts/deprecated/java_convert_matrix.m, scripts/deprecated/java_debug.m,
scripts/deprecated/java_unsigned_conversion.m, scripts/deprecated/shell_cmd.m,
scripts/general/dblquad.m, scripts/general/display.m,
scripts/general/genvarname.m, scripts/general/idivide.m,
scripts/general/interp1.m, scripts/general/interp2.m,
scripts/general/interp3.m, scripts/general/interpn.m, scripts/general/isa.m,
scripts/general/profexplore.m, scripts/general/profile.m,
scripts/general/quadgk.m, scripts/general/randi.m, scripts/general/structfun.m,
scripts/general/subsindex.m, scripts/general/triplequad.m,
scripts/geometry/griddata.m, scripts/geometry/griddata3.m,
scripts/geometry/griddatan.m, scripts/geometry/voronoi.m, scripts/help/help.m,
scripts/help/lookfor.m, scripts/image/cmpermute.m, scripts/image/colormap.m,
scripts/image/image.m, scripts/image/imagesc.m, scripts/image/imfinfo.m,
scripts/image/imformats.m, scripts/image/imread.m, scripts/image/imshow.m,
scripts/image/imwrite.m, scripts/image/ind2gray.m, scripts/image/lines.m,
scripts/image/rgb2ind.m, scripts/image/spinmap.m, scripts/io/dlmwrite.m,
scripts/io/strread.m, scripts/io/textread.m, scripts/io/textscan.m,
scripts/java/javaclasspath.m, scripts/java/usejava.m,
scripts/miscellaneous/bzip2.m, scripts/miscellaneous/computer.m,
scripts/miscellaneous/copyfile.m, scripts/miscellaneous/debug.m,
scripts/miscellaneous/dos.m, scripts/miscellaneous/edit.m,
scripts/miscellaneous/gzip.m, scripts/miscellaneous/license.m,
scripts/miscellaneous/mkoctfile.m, scripts/miscellaneous/movefile.m,
scripts/miscellaneous/parseparams.m, scripts/miscellaneous/unix.m,
scripts/optimization/fminbnd.m, scripts/optimization/fminsearch.m,
scripts/optimization/fminunc.m, scripts/optimization/fsolve.m,
scripts/optimization/fzero.m, scripts/optimization/glpk.m,
scripts/optimization/lsqnonneg.m, scripts/optimization/optimset.m,
scripts/optimization/pqpnonneg.m, scripts/pkg/pkg.m, scripts/plot/allchild.m,
scripts/plot/ancestor.m, scripts/plot/area.m, scripts/plot/axis.m,
scripts/plot/bar.m, scripts/plot/barh.m, scripts/plot/box.m,
scripts/plot/caxis.m, scripts/plot/cla.m, scripts/plot/clabel.m,
scripts/plot/clf.m, scripts/plot/close.m, scripts/plot/colorbar.m,
scripts/plot/daspect.m, scripts/plot/ezmesh.m, scripts/plot/ezmeshc.m,
scripts/plot/ezsurf.m, scripts/plot/ezsurfc.m, scripts/plot/findall.m,
scripts/plot/findobj.m, scripts/plot/gcbo.m, scripts/plot/gcf.m,
scripts/plot/gco.m, scripts/plot/grid.m, scripts/plot/guihandles.m,
scripts/plot/hdl2struct.m, scripts/plot/hidden.m, scripts/plot/hold.m,
scripts/plot/isonormals.m, scripts/plot/isosurface.m, scripts/plot/legend.m,
scripts/plot/mesh.m, scripts/plot/meshc.m, scripts/plot/meshz.m,
scripts/plot/newplot.m, scripts/plot/orient.m, scripts/plot/pareto.m,
scripts/plot/patch.m, scripts/plot/pbaspect.m, scripts/plot/pcolor.m,
scripts/plot/plot.m, scripts/plot/print.m,
scripts/plot/private/__add_default_menu__.m, scripts/plot/quiver.m,
scripts/plot/quiver3.m, scripts/plot/refreshdata.m, scripts/plot/saveas.m,
scripts/plot/scatter.m, scripts/plot/scatter3.m, scripts/plot/shading.m,
scripts/plot/shrinkfaces.m, scripts/plot/slice.m, scripts/plot/stem.m,
scripts/plot/stem3.m, scripts/plot/struct2hdl.m, scripts/plot/subplot.m,
scripts/plot/surf.m, scripts/plot/surfc.m, scripts/plot/surfl.m,
scripts/plot/tetramesh.m, scripts/plot/uigetfile.m, scripts/plot/uimenu.m,
scripts/plot/uiputfile.m, scripts/plot/waterfall.m, scripts/plot/whitebg.m,
scripts/plot/xlim.m, scripts/plot/ylim.m, scripts/plot/zlim.m,
scripts/polynomial/conv.m, scripts/polynomial/polyout.m,
scripts/polynomial/splinefit.m, scripts/set/ismember.m, scripts/set/powerset.m,
scripts/set/setdiff.m, scripts/set/union.m, scripts/set/unique.m,
scripts/signal/detrend.m, scripts/signal/filter2.m, scripts/signal/freqz.m,
scripts/signal/periodogram.m, scripts/signal/spectral_adf.m,
scripts/signal/spectral_xdf.m, scripts/sparse/eigs.m, scripts/sparse/svds.m,
scripts/specfun/legendre.m, scripts/special-matrix/gallery.m,
scripts/statistics/base/mean.m, scripts/statistics/base/moment.m,
scripts/statistics/tests/cor_test.m,
scripts/statistics/tests/kolmogorov_smirnov_test.m,
scripts/statistics/tests/kolmogorov_smirnov_test_2.m,
scripts/statistics/tests/kruskal_wallis_test.m,
scripts/statistics/tests/prop_test_2.m, scripts/statistics/tests/sign_test.m,
scripts/statistics/tests/t_test.m, scripts/statistics/tests/t_test_2.m,
scripts/statistics/tests/t_test_regression.m,
scripts/statistics/tests/u_test.m, scripts/statistics/tests/var_test.m,
scripts/statistics/tests/welch_test.m,
scripts/statistics/tests/wilcoxon_test.m, scripts/statistics/tests/z_test.m,
scripts/statistics/tests/z_test_2.m, scripts/strings/base2dec.m,
scripts/strings/index.m, scripts/strings/isstrprop.m,
scripts/strings/mat2str.m, scripts/strings/regexptranslate.m,
scripts/strings/rindex.m, scripts/strings/str2num.m, scripts/strings/strcat.m,
scripts/strings/strjust.m, scripts/strings/strmatch.m,
scripts/strings/validatestring.m, scripts/testfun/demo.m,
scripts/testfun/example.m, scripts/testfun/test.m, scripts/time/addtodate.m,
scripts/time/asctime.m, scripts/time/datestr.m, scripts/time/datetick.m,
scripts/time/weekday.m, scripts/ui/errordlg.m, scripts/ui/helpdlg.m,
scripts/ui/inputdlg.m, scripts/ui/listdlg.m, scripts/ui/msgbox.m,
scripts/ui/questdlg.m, scripts/ui/warndlg.m: Use new @qcode macro.
| author | Rik <rik@octave.org> |
|---|---|
| date | Mon, 19 Aug 2013 20:46:38 -0700 |
| parents | e7a059a9a644 |
| children | d63878346099 |
| rev | line source |
|---|---|
|
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maint: update copyright notices for 2012
John W. Eaton <jwe@octave.org>
parents:
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diff
changeset
|
1 @c Copyright (C) 1996-2012 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. | |
| 9 @c | |
| 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. | |
| 14 @c | |
| 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 Evaluation |
| 3294 | 20 @chapter Evaluation |
| 21 | |
| 22 Normally, you evaluate expressions simply by typing them at the Octave | |
| 23 prompt, or by asking Octave to interpret commands that you have saved in | |
| 24 a file. | |
| 25 | |
| 26 Sometimes, you may find it necessary to evaluate an expression that has | |
| 6641 | 27 been computed and stored in a string, which is exactly what the |
|
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28 @code{eval} function lets you do. |
| 3294 | 29 |
| 3371 | 30 @DOCSTRING(eval) |
| 3294 | 31 |
| 6641 | 32 @menu |
| 33 * Calling a Function by its Name:: | |
| 34 * Evaluation in a Different Context:: | |
| 35 @end menu | |
| 36 | |
| 37 @node Calling a Function by its Name | |
| 38 @section Calling a Function by its Name | |
| 3294 | 39 |
| 7001 | 40 The @code{feval} function allows you to call a function from a string |
|
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41 containing its name. This is useful when writing a function that needs to |
|
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42 call user-supplied functions. The @code{feval} function takes the name |
| 6641 | 43 of the function to call as its first argument, and the remaining |
| 44 arguments are given to the function. | |
| 45 | |
| 46 The following example is a simple-minded function using @code{feval} | |
| 47 that finds the root of a user-supplied function of one variable using | |
| 48 Newton's method. | |
| 3294 | 49 |
| 50 @example | |
| 51 function result = newtroot (fname, x) | |
| 52 | |
| 53 # usage: newtroot (fname, x) | |
| 54 # | |
| 55 # fname : a string naming a function f(x). | |
| 56 # x : initial guess | |
| 57 | |
| 58 delta = tol = sqrt (eps); | |
| 59 maxit = 200; | |
| 60 fx = feval (fname, x); | |
| 61 for i = 1:maxit | |
| 62 if (abs (fx) < tol) | |
| 63 result = x; | |
| 64 return; | |
| 65 else | |
| 66 fx_new = feval (fname, x + delta); | |
| 67 deriv = (fx_new - fx) / delta; | |
| 68 x = x - fx / deriv; | |
| 69 fx = fx_new; | |
| 70 endif | |
| 71 endfor | |
| 72 | |
| 73 result = x; | |
| 74 | |
| 75 endfunction | |
| 76 @end example | |
| 77 | |
| 78 Note that this is only meant to be an example of calling user-supplied | |
| 79 functions and should not be taken too seriously. In addition to using a | |
| 80 more robust algorithm, any serious code would check the number and type | |
| 81 of all the arguments, ensure that the supplied function really was a | |
|
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82 function, etc. @xref{Predicates for Numeric Objects}, |
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83 for a list of predicates for numeric objects, and @pxref{Status of |
| 3294 | 84 Variables}, for a description of the @code{exist} function. |
| 6549 | 85 |
| 6641 | 86 @DOCSTRING(feval) |
| 87 | |
| 6863 | 88 A similar function @code{run} exists for calling user script files, that |
| 89 are not necessarily on the user path | |
| 90 | |
| 91 @DOCSTRING(run) | |
| 92 | |
| 6641 | 93 @node Evaluation in a Different Context |
| 94 @section Evaluation in a Different Context | |
| 95 | |
| 96 Before you evaluate an expression you need to substitute | |
| 97 the values of the variables used in the expression. These | |
| 98 are stored in the symbol table. Whenever the interpreter | |
| 99 starts a new function it saves the current symbol table | |
| 100 and creates a new one, initializing it with the list of | |
| 101 function parameters and a couple of predefined variables | |
| 102 such as @code{nargin}. Expressions inside the function use the | |
| 103 new symbol table. | |
| 104 | |
| 105 Sometimes you want to write a function so that when you | |
| 106 call it, it modifies variables in your own context. This | |
| 107 allows you to use a pass-by-name style of function, | |
| 108 which is similar to using a pointer in programming languages such | |
| 109 as C. | |
| 110 | |
| 111 Consider how you might write @code{save} and @code{load} as | |
|
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112 m-files. For example: |
| 6641 | 113 |
| 114 @example | |
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115 @group |
| 6641 | 116 function create_data |
| 117 x = linspace (0, 10, 10); | |
| 118 y = sin (x); | |
| 119 save mydata x y | |
| 120 endfunction | |
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121 @end group |
| 6641 | 122 @end example |
| 123 | |
| 8828 | 124 With @code{evalin}, you could write @code{save} as follows: |
| 6641 | 125 |
| 126 @example | |
|
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127 @group |
| 6641 | 128 function save (file, name1, name2) |
| 129 f = open_save_file (file); | |
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130 save_var (f, name1, evalin ("caller", name1)); |
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131 save_var (f, name2, evalin ("caller", name2)); |
| 6641 | 132 endfunction |
|
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133 @end group |
| 6641 | 134 @end example |
| 135 | |
| 136 @noindent | |
| 137 Here, @samp{caller} is the @code{create_data} function and @code{name1} | |
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138 is the string @qcode{"x"}, which evaluates simply as the value of @code{x}. |
| 6641 | 139 |
| 140 You later want to load the values back from @code{mydata} | |
| 141 in a different context: | |
| 142 | |
| 143 @example | |
|
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144 @group |
| 6641 | 145 function process_data |
| 146 load mydata | |
| 147 @dots{} do work @dots{} | |
| 148 endfunction | |
|
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149 @end group |
| 6641 | 150 @end example |
| 151 | |
| 152 @noindent | |
| 153 With @code{assignin}, you could write @code{load} as follows: | |
| 154 | |
| 155 @example | |
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156 @group |
| 6641 | 157 function load (file) |
| 158 f = open_load_file (file); | |
| 159 [name, val] = load_var (f); | |
| 160 assignin ("caller", name, val); | |
| 161 [name, val] = load_var (f); | |
| 162 assignin ("caller", name, val); | |
| 163 endfunction | |
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164 @end group |
| 6641 | 165 @end example |
| 166 | |
| 167 @noindent | |
| 168 Here, @samp{caller} is the @code{process_data} function. | |
| 169 | |
| 170 You can set and use variables at the command prompt | |
| 171 using the context @samp{base} rather than @samp{caller}. | |
| 172 | |
| 173 These functions are rarely used in practice. One | |
| 174 example is the @code{fail (@samp{code}, @samp{pattern})} function | |
| 175 which evaluates @samp{code} in the caller's context and | |
| 176 checks that the error message it produces matches | |
| 177 the given pattern. Other examples such as @code{save} and @code{load} | |
|
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178 are written in C++ where all Octave variables |
| 6641 | 179 are in the @samp{caller} context and @code{evalin} is not needed. |
| 180 | |
| 6549 | 181 @DOCSTRING(evalin) |
| 182 | |
| 183 @DOCSTRING(assignin) |