%-------------------------------------------------------------------------------
% UF Sparse Matrix Collection, Tim Davis
% http://www.cise.ufl.edu/research/sparse/matrices/Harvard_Seismology/JP
% name: Harvard_Seismology/JP
% [Earth's crust underneath Japan, Harvard Seismology Group]
% id: 2757
% date: 2015
% author: P. Bogiatzis, M. Ishii
% ed: T. Davis
% fields: name title A id date author ed kind notes
% kind: tomography problem
%-------------------------------------------------------------------------------
% notes:
% Earth's crust underneath Japan, Harvard Seismology Group.               
%                                                                         
% This matrix represents the forward operator of a linearized seismic     
% tomography problem for imaging Japan's crust and upper mantle.  The     
% rows of the matrix correspond to 87,616 P-wave ray paths, from 125      
% moderate size earthquakes (stars), deeper that ~150 km that occurred    
% the last decade, and recorded from seismic stations of the Hi-net       
% array (triangles). The 3-Dimensional space is parameterized using a     
% grid of 67,320 parameters that correspond to the columns of the matrix. 
%                                                                         
% The matrix is structurally and numerically rank deficient.  This is     
% because some parts of the Earth are not imaged well from the data,      
% due to the lack of signals (earthquakes) and receivers (seismic stations
% in those areas.  This leads to an under-determined part of the system.  
% Other parts of the problem are overdetermined, because deep earthquakes 
% repeat in the same region of the Earth, over time, and the seismic      
% stations do not move.  Repeated earthquakes from the same source        
% are recorded by the same seismic stations, leading to an over-          
% determined problem for those regions of the Earth.                      
%                                                                         
% In MATLAB, cs_dmspy(Problem.A) displays these two parts of the matrix,  
% using a function from CSparse, available at http://suitesparse.com.     
%                                                                         
% Petros Bogiatzis, Miaki Ishii, Harvard Seismology Group, 2015           
% http://www.seismology.harvard.edu                                       
%                                                                         
% Bogiatzis, P., & Ishii, M., 2014. Resolution Analysis and Jointly       
% Inverted P-and S-Wave Models of Japan's Crust and Upper Mantle.         
% American Geophysical Union, Fall Meeting 2014, S33A-4501.               
%-------------------------------------------------------------------------------
