1function Opout=operatorappr(Op,T)
2%-*- texinfo -*-
3%@deftypefn {Function} operatorappr
4%@verbatim
5%OPERATORAPPR  Best approximation by operator
6%   Usage: c=operatorappr(Op,K);
7%
8%   Opout=OPERATORAPPR(Opin,T) computes the an operator Opout of the
9%   same type as Opin that best approximates the matrix T in the
10%   Frobenious norm of the matrix (the Hilbert-Schmidt norm of the
11%   operator).
12%
13%   For some operator classes, the approximation is always exact, so that
14%   operator(Opout,f) computes the exact same result as T'*f.
15%
16%@end verbatim
17%@strong{Url}: @url{http://ltfat.github.io/doc/operators/operatorappr.html}
18%@seealso{operatornew, operator, operatoreigs}
19%@end deftypefn
20
21% Copyright (C) 2005-2016 Peter L. Soendergaard <peter@sonderport.dk>.
22% This file is part of LTFAT version 2.3.1
23%
24% This program is free software: you can redistribute it and/or modify
25% it under the terms of the GNU General Public License as published by
26% the Free Software Foundation, either version 3 of the License, or
27% (at your option) any later version.
28%
29% This program is distributed in the hope that it will be useful,
30% but WITHOUT ANY WARRANTY; without even the implied warranty of
31% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
32% GNU General Public License for more details.
33%
34% You should have received a copy of the GNU General Public License
35% along with this program.  If not, see <http://www.gnu.org/licenses/>.
36
37if nargin<2
38  error('%s: Too few input parameters.',upper(mfilename));
39end;
40
41if ~isstruct(Op)
42  error('%s: First argument must be a operator definition structure.',upper(mfilename));
43end;
44
45switch(Op.type)
46  case 'framemul'
47    s=framemulappr(Op.Fa,Op.Fs,T);
48    Opout=operatornew('framemul',Op.Fa,Op.Fs,s);
49  case 'spread'
50    s=spreadfun(T);
51    Opout=operatornew('spread',s);
52end;
53
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56