jacob_element

 function d=jacob_element(func,element,args)
 returns an entry of the finite differences approximation to the jacobian of func

 INPUTS
    func       [function name]    string with name of the function
    element    [int]              the index showing the element within the jacobian that should be returned
    args       [cell array]       arguments provided to func

 OUTPUTS
    d          [double]           jacobian[element]

 SPECIAL REQUIREMENTS
    none

0001 function d=jacob_element(func,element,args)
0002 % function d=jacob_element(func,element,args)
0003 % returns an entry of the finite differences approximation to the jacobian of func
0004 %
0005 % INPUTS
0006 %    func       [function name]    string with name of the function
0007 %    element    [int]              the index showing the element within the jacobian that should be returned
0008 %    args       [cell array]       arguments provided to func
0009 %
0010 % OUTPUTS
0011 %    d          [double]           jacobian[element]
0012 %
0013 % SPECIAL REQUIREMENTS
0014 %    none
0015 
0016 % Copyright (C) 2010-2011 Dynare Team
0017 %
0018 % This file is part of Dynare.
0019 %
0020 % Dynare is free software: you can redistribute it and/or modify
0021 % it under the terms of the GNU General Public License as published by
0022 % the Free Software Foundation, either version 3 of the License, or
0023 % (at your option) any later version.
0024 %
0025 % Dynare is distributed in the hope that it will be useful,
0026 % but WITHOUT ANY WARRANTY; without even the implied warranty of
0027 % MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
0028 % GNU General Public License for more details.
0029 %
0030 % You should have received a copy of the GNU General Public License
0031 % along with Dynare.  If not, see <http://www.gnu.org/licenses/>.
0032 
0033 func = str2func(func);
0034 
0035 h=10e-6;
0036 pargs=args;
0037 margs=args;
0038 % length(args) is used instead of size(args, 2) to avoid to transpose column vectors
0039 for i=1:length(args)
0040     if i==element
0041         pargs{i} = pargs{i} + h;
0042         margs{i} = margs{i} - h;
0043     end
0044 end
0045 d=(func(pargs{:})...
0046    -func(margs{:}))/(2*h);