spinteract.m

该算法是用于量子运算的matlab程序

% spinteract   Interaction between two qudits; sparse version
%   spinteract (op1,op2,n1,n2,n) gives an operator
%   acting on qudits n1 and n2, respectively, with
%   operators op1 and op2. n is the number of qudits.
%   If argument n is omitted than the default
%   is taken to be the value of global variable N.
%   The dimension of the qudit is obtained from the size of op1.
%   (For qubits op1 is 2x2, for qutrits it is 3x3, etc.)

% Copyright (C) 2005  Geza Toth    E.mail: [e-mail]
%
% 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; see gpl.txt
% of this subroutine package.
%
% This program 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 program; if not, write to the Free Software
% Foundation, Inc., 51 Franklin Street, Fifth Floor, 
% Boston, MA  02110-1301, USA.

function op=spinteract(op1,op2,n1,n2,varargin)

if isempty(varargin),
    global N;
else
    if length(varargin)~=1,
        error('Wrong number of input arguments.')
    end %if
    N=varargin{1};
end %if

d=max(size(op1));

m1=min(n1,n2);
m2=max(n1,n2);
op=mkron(speye(d^(N-m2)),op2,speye(d^(m2-m1-1)),op1,speye(d^(m1-1)));