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+% function f = local_TV3D_chambolle(f, lambda, niter)
+% apply local total variation usiniter matlab functions, it uses chambolle
+% solver -> faster but more memory demanding 
+%  Inputs: f - 3D array to be regularized 
+%          lambda - constant to be tuned
+%          niter - number of iterations 
+
+
+%*-----------------------------------------------------------------------*
+%|                                                                       |
+%|  Except where otherwise noted, this work is licensed under a          |
+%|  Creative Commons Attribution-NonCommercial-ShareAlike 4.0            |
+%|  International (CC BY-NC-SA 4.0) license.                             |
+%|                                                                       |
+%|  Copyright (c) 2017 by Paul Scherrer Institute (http://www.psi.ch)    |
+%|                                                                       |
+%|       Author: CXS group, PSI                                          |
+%*-----------------------------------------------------------------------*
+% You may use this code with the followiniter provisions:
+%
+% If the code is fully or partially redistributed, or rewritten in another
+%   computiniter laniteruage this notice should be included in the redistribution.
+%
+% If this code, or subfunctions or parts of it, is used for research in a 
+%   publication or if it is fully or partially rewritten for another 
+%   computiniter laniteruage the authors and institution should be acknowledged 
+%   in written form in the publication: “Data processiniter was carried out 
+%   usiniter the “cSAXS matlab package” developed by the CXS group,
+%   Paul Scherrer Institut, Switzerland.” 
+%   Variations on the latter text can be incorporated upon discussion with 
+%   the CXS group if needed to more specifically reflect the use of the package 
+%   for the published work.
+%
+% A publication that focuses on describiniter features, or parameters, that
+%    are already existiniter in the code should be first discussed with the
+%    authors.
+%   
+% This code and subroutines are part of a continuous development, they 
+%    are provided “as they are” without guarantees or liability on part
+%    of PSI or the authors. It is the user responsibility to ensure its 
+%    proper use and the correctness of the results.
+
+
+function x = local_TV3D_chambolle(x,lambda, niter)
+    [M,N,O] = size(x); 
+    
+    if lambda == 0
+        return
+    end
+    
+    x0 = x; 
+    xi = zeros(M,N,O,3, class(x));
+    tau=2/8;
+    %%% INNER LOOP
+    for iinner = 1:niter
+        % chambolle step
+        gdv = grad( div(xi) - x/lambda );
+
+        %% isotropic 
+%       d = sqrt(sum(gdv.^2,3));
+        %% anisotropic 
+        d = sum( abs(gdv), 4);
+        xi = bsxfun(@times, xi + tau*gdv, 1 ./ ( 1+tau*d ));
+        % reconstruct
+        x = x - lambda*div( xi   );
+
+    end
+    
+    % prevent pushing values to zero by the TV regularization 
+    x = sum(x0(:).* x(:)) / sum(x(:).^2) * x; 
+    
+end
+
+function fd = div(P)
+
+% div - divergence (backward difference)
+%
+%	fd = div(P);
+
+	Px = P(:,:,:,1);
+	Py = P(:,:,:,2);
+	Pz = P(:,:,:,3);
+
+
+    fx = Px-Px([1 1:end-1],:,:);
+    fy = Py-Py(:,[1 1:end-1],:);
+    fz = Pz-Pz(:,:,[1 1:end-1]);
+    fd = fx+fy+fz;
+
+end
+
+function f = grad(M)
+
+% grad - gradient, forward differences
+%   g = grad(M);
+
+    fx = M([2:end end],:,:)-M;
+    fy = M(:,[2:end end],:)-M;
+    fz = M(:,:,[2:end end])-M;
+
+    f = cat(4,fx,fy,fz);
+
+end