  This is the documentation of the tomographic X-ray data of a lotus root,
filled with four different attenuating objects, of different sizes. Data are
available at www.fips.fi/dataset.php, and can be freely used for scientific
purposes with appropriate references to them, and to this document in
http://arxiv.org/arXiv. The data set consists of (1) the X-ray sinogram of a
single 2D slice of the lotus root with two different resolutions and (2) the
corresponding measurement matrices modeling the linear operation of the X-ray
transform. Each of these sinograms was obtained from a measured 360-projection
fan-beam sinogram by down-sampling and taking logarithms. The original
(measured) sinogram is also provided in its original form and resolution.
