SIRT_CUDA
=========

This is a GPU implementation of the Simultaneous Iterative Reconstruction Technique (SIRT) for 2D data sets. It takes projection data and an initial reconstruction as input, and returns the reconstruction after a specified number of SIRT iterations.

Supported geometries: parallel, parallel_vec, fanflat, fanflat_vec.

Configuration options
---------------------

================================	========	======
name 					type 		description
================================	========	======
cfg.ProjectionDataId 			required 	The astra_mex_data2d ID of the projection data
cfg.ReconstructionDataId 		required 	The astra_mex_data2d ID of the reconstruction data. The content of this when starting SIRT is used as the initial reconstruction.
cfg.option.SinogramMaskId 		optional 	If specified, the astra_mex_data2d ID of a projection-data-sized volume to be used as a mask.
cfg.option.ReconstructionMaskId 	optional 	If specified, the astra_mex_data2d ID of a volume-data-sized volume to be used as a mask.
cfg.option.MinConstraint 		optional 	If specified, all values below MinConstraint will be set to MinConstraint. This can, for example, be used to enforce non-negative reconstructions.
cfg.option.MaxConstraint 		optional 	If specified, all values above MaxConstraint will be set to MaxConstraint.
cfg.option.GPUindex 			optional 	Specifies which GPU to use. Default = 0.
cfg.option.DetectorSuperSampling 	optional 	Specifies the amount of detector supersampling, i.e. how many rays are cast per detector.
cfg.option.PixelSuperSampling 		optional 	Specifies the amount of pixel supersampling, i.e. how many (one dimension) subpixels are generated from a single parent pixel.
================================	========	======

Example
-------

.. code-block:: matlab

	%% create phantom
	V_exact = phantom(256);

	%% create geometries
	proj_geom = astra_create_proj_geom('parallel', 1.0, 256, linspace2(0,pi,180));
	vol_geom = astra_create_vol_geom(256,256);

	%% create forward projection
	[sinogram_id, sinogram] = astra_create_sino_cuda(V_exact, proj_geom, vol_geom);

	%% reconstruct
	recon_id = astra_mex_data2d('create', '-vol', vol_geom, 0);
	cfg = astra_struct('SIRT_CUDA');
	cfg.ProjectionDataId = sinogram_id;
	cfg.ReconstructionDataId = recon_id;
	cfg.option.MinConstraint = 0;
	cfg.option.MaxConstraint = 255;
	sirt_id = astra_mex_algorithm('create', cfg);
	astra_mex_algorithm('iterate', sirt_id, 100);
	V = astra_mex_data2d('get', recon_id);
	imshow(V, []);

	%% garbage disposal
	astra_mex_data2d('delete', sinogram_id, recon_id);
	astra_mex_algorithm('delete', sirt_id);

Extra features
--------------

SIRT_CUDA supports astra_mex_algorithm('get_res_norm') to get the 2-norm of the difference between the projection data and the projection of the reconstruction. (The square root of the sum of squares of differences.)