## Priebel/208bit

Quadratic sieve; factoring a 208bit number. D. Priebel, Tenn. Tech Univ

Name | 208bit |
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Group | Priebel |

Matrix ID | 2255 |

Num Rows | 24,430 |

Num Cols | 24,421 |

Nonzeros | 299,756 |

Pattern Entries | 299,756 |

Kind | Combinatorial Problem |

Symmetric | No |

Date | 2009 |

Author | D. Priebel |

Editor | T. Davis |

SVD Statistics | |
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Matrix Norm | 1.908958e+02 |

Minimum Singular Value | 0 |

Condition Number | Inf |

Rank | 22,981 |

sprank(A)-rank(A) | 0 |

Null Space Dimension | 1,440 |

Full Numerical Rank? | no |

Download Singular Values | MATLAB |

Download | MATLAB Rutherford Boeing Matrix Market |
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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 = 239380926372595066574100671394554319947805305453767699448870971 (208-bits) passes primality test, n is composite, continuing... 1) Initial bound: 650000, pi(650000) estimate: 48562, largest found: 592903 (actual bound) 2) Number of quadratic residues estimate: 32376, actual number found: 24420 3) Modular square roots found: 48840(2x residues) 4) Constructing smooth number list [sieving] (can take a while)... Sieving for: 24430 5. Constructing a matrix of size: 24430x24421 Set a total of 299756 exponents, with 12070 negatives Matrix solution found with: 8741 combinations Divisor: 12216681953629826483019726942851 (probably prime) Divisor: 19594594283554225566102143686121 (probably prime) |