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+% -----------------------------------------------------------------------
+% This file is part of the ASTRA Toolbox
+% 
+% Copyright: 2010-2015, iMinds-Vision Lab, University of Antwerp
+%            2014-2015, CWI, Amsterdam
+% License: Open Source under GPLv3
+% Contact: astra@uantwerpen.be
+% Website: http://sf.net/projects/astra-toolbox
+% -----------------------------------------------------------------------
+
+% This sample illustrates the use of opTomo.
+%
+% opTomo is a wrapper around the FP and BP operations of the ASTRA Toolbox,
+% to allow you to use them as you would a matrix.
+%
+% This class requires the Spot Linear-Operator Toolbox to be installed.
+% You can download this at http://www.cs.ubc.ca/labs/scl/spot/
+
+% load a phantom image
+im = phantom(256);
+% and flatten it to a vector
+x = im(:);
+
+%% Setting up the geometry
+% projection geometry
+proj_geom = astra_create_proj_geom('parallel', 1, 256, linspace2(0,pi,180));
+% object dimensions
+vol_geom  = astra_create_vol_geom(256,256);
+
+%% Generate projection data
+% Create the Spot operator for ASTRA using the GPU.
+W = opTomo('cuda', proj_geom, vol_geom);
+
+p = W*x;
+
+% reshape the vector into a sinogram
+sinogram = reshape(p, W.proj_size);
+imshow(sinogram, []);
+
+
+%% Reconstruction
+% We use a least squares solver lsqr from Matlab to solve the 
+% equation W*x = p.
+% Max number of iterations is 100, convergence tolerance of 1e-6.
+y = lsqr(W, p, 1e-6, 100);
+
+% the output is a vector, so we reshape it into an image
+reconstruction = reshape(y, W.vol_size);
+
+subplot(1,3,1);
+imshow(reconstruction, []);
+title('Reconstruction');
+
+subplot(1,3,2);
+imshow(im, []);
+title('Ground truth');
+
+% The transpose of the operator corresponds to the backprojection.
+backProjection = W'*p;
+subplot(1,3,3);
+imshow(reshape(backProjection, W.vol_size), []);
+title('Backprojection');