[r8778]: trunk / octave-forge / main / symbolic / inst / findsym.m  Maximize  Restore  History

Download this file

93 lines (81 with data), 2.5 kB

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
## Copyright (C) 2003 Willem J. Atsma <watsma@users.sf.net>
##
## This program is free software; you can redistribute it and/or
## modify it under the terms of the GNU General Public
## License as published by the Free Software Foundation;
## either version 2, or (at your option) any later version.
##
## This software is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied
## warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
## PURPOSE. See the GNU General Public License for more
## details.
##
## You should have received a copy of the GNU General Public
## License along with this software; see the file COPYING. If not,
## see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {@var{vars} =} findsym (@var{f}, @var{n})
## Find symbols in expression @var{f} and return them comma-separated in
## string @var{vars}. The symbols are sorted in alphabetic order. If @var{n}
## is specified, the @var{n} symbols closest to "x" are returned.
##
## Example:
## @example
## symbols
## x = sym ("x");
## y = sym ("y");
## f = x^2+3*x*y-y^2;
## vars = findsym (f);
## vars2 = findsym (f,1);
## @end example
##
## This is intended for m****b compatibility, calls findsymbols().
## @seealso{findsymbols}
## @end deftypefn
function VARS = findsym(F,Nout)
symlist = findsymbols(F);
Nlist = length(symlist);
if Nlist==0
warning("No symbols were found.")
VARS = "";
return
endif
if exist("Nout")!=1
VARS = disp(symlist{1});
for i=2:Nlist
VARS = [VARS "," disp(symlist{i})];
endfor
return
else
## If Nout is specified, sort anew from x.
symstrings = disp(symlist{1});
for i=2:Nlist
symstrings = [symstrings ; disp(symlist{i})];
endfor
symasc = toascii(symstrings);
if Nlist<Nout
warning("Asked for %d, variables, only %d found.",Nout,Nlist);
Nout=Nlist;
endif
symasc(:,1) = abs(toascii("x")-symasc(:,1));
## Sort by creating an equivalent number for each entry
Nc = length(symasc(1,:));
powbase=zeros(Nc,1); powbase(Nc)=1;
for i=(Nc-1):-1:1
powbase(i) = powbase(i+1)*128;
endfor
[xs,I]=sort(symasc*powbase);
VARS = deblank(symstrings(I(1),:));
for i=2:Nout
VARS = [VARS "," deblank(symstrings(I(i),:))];
endfor
endif
endfunction
%!test
%! symbols
%! x=sym("x"); y=sym("y"); f=x^2+3*x*y-y^2;
%! vars = findsym (f);
%! assert(vars, 'x,y');
%! vars2 = findsym (f,1);
%! assert(vars2, 'x');