%-------------------------------------------------------------------------------
% UF Sparse Matrix Collection, Tim Davis
% http://www.cise.ufl.edu/research/sparse/matrices/Priebel/176bit
% name: Priebel/176bit
% [Quadratic sieve; factoring a 176bit number. D. Priebel, Tenn. Tech Univ]
% id: 2253
% date: 2009
% author: D. Priebel
% ed: T. Davis
% fields: name title A id date author ed kind notes aux
% aux: factor_base smooth_number solution
% kind: combinatorial problem
%-------------------------------------------------------------------------------
% notes:
% Each column in the matrix corresponds to a number in the factor base     
% less than some bound B.  Each row corresponds to a smooth number (able   
% to be completely factored over the factor base).  Each value in a row    
% binary vector corresponds to the exponent of the factor base mod 2.      
% For example:                                                             
%                                                                          
%     factor base: 2 7 23                                                  
%     smooth numbers: 46, 28, 322                                          
%     2^1       * 23^1 = 46                                                
%     2^2 * 7^1        = 28                                                
%     2^1 * 7^1 * 23^1 = 322                                               
%     Matrix:                                                              
%         101                                                              
%         010                                                              
%         111                                                              
%                                                                          
% A solution to the matrix is considered to be a set of rows which when    
% combined in GF2 produce a null vector. Thus, if you multiply each of     
% the smooth numbers which correspond to that particular set of rows you   
% will get a number with only even exponents, making it a perfect          
% square. In the above example you can see that combining the 3 vectors    
% results in a null vector and, indeed, it is a perfect square: 644^2.     
%                                                                          
% Problem.A: A GF(2) matrix constructed from the exponents of the          
% factorization of the smooth numbers over the factor base. A solution of  
% this matrix is a kernel (nullspace). Such a solution has a 1/2 chance of 
% being a factorization of N.                                              
%                                                                          
% Problem.aux.factor_base: The factor base used. factor_base(j) corresponds
% to column j of the matrix. Note that a given column may or may not have  
% nonzero elements in the matrix.                                          
%                                                                          
% Problem.aux.smooth_number: The smooth numbers, smooth over the factor    
% base.  smooth_number(i) corresponds to row i of the matrix.              
%                                                                          
% Problem.aux.solution: A sample solution to the matrix. Combine, in GF(2) 
% the rows with these indicies to produce a solution to the matrix with the
% additional property that it factors N (a matrix solution only has 1/2    
% probability of factoring N).                                             
%                                                                          
% Problem specific information:                                            
%                                                                          
% n = 73363722971930954428433124842779099222294372095286387 (176-bits)     
% passes primality test, n is composite, continuing...                     
% 1) Initial bound: 180000, pi(180000) estimate: 14875,                    
%     largest found: 162359 (actual bound)                                 
% 2) Number of quadratic residues estimate: 9918, actual number found: 7431
% 3) Modular square roots found: 14862(2x residues)                        
% 4) Constructing smooth number list [sieving] (can take a while)...       
% Sieving for: 7441                                                        
% 5. Constructing a matrix of size: 7441x7432                              
% Set a total of 82270 exponents, with 3725 negatives                      
% Matrix solution found with: 2983 combinations                            
% Divisor: 236037985789994529800050193 (probably prime)                    
% Divisor: 310813205452462332837525059 (probably prime)                    
%-------------------------------------------------------------------------------
