# CGLS3D_CUDA¶

This is a GPU implementation of the CGLS algorithm for 3D data sets. It takes projection data and an initial reconstruction as input, and returns the reconstruction after a specified number of CGLS iterations.

The internal state of the CGLS algorithm is reset every time astra_mex_algorithm(‘iterate’) is called. This implies that running CGLS for N iterations and then running it for another N iterations may yield different results from running it 2N iterations at once.

Supported geometries: all 3D geometries.

## Configuration options¶

name | type | description |
---|---|---|

cfg.ProjectionDataId | required | The astra_mex_data3d ID of the projection data |

cfg.ReconstructionDataId | required | The astra_mex_data3d ID of the reconstruction data. The content of this when starting SIRT3D_CUDA is used as the initial reconstruction. |

cfg.option.ReconstructionMaskId | optional | If specified, the astra_mex_data3d ID of a volume-data-sized volume to be used as a mask. It should only have values 0.0 and 1.0. See the section on [Masks] for details. |

cfg.option.GPUindex | optional | The index (zero-based) of the GPU to use. (default: 0) |

cfg.option.DetectorSuperSampling | optional | For the forward projection, DetectorSuperSampling^2 rays will be used. This should only be used if your detector pixels are larger than the voxels in the reconstruction volume. (default: 1) |

cfg.option.VoxelSuperSampling | optional | For the backward projection, VoxelSuperSampling^3 rays will be used. This should only be used if your voxels in the reconstruction volume are larger than the detector pixels. (default: 1) |

## Extra features¶

CGLS3D_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.)