jeanluct/cbraid

cbraid/braiding are C++ libraries for computations on braid groups

cbraid's Issues

Confusing

If someone wanted to use this as a protocol for encrypted communications, they'd never figure out how to do that without a humongous computer science background

Bug in sliding circuit set

From Bert Wiest: there seems to be a bug in the Sliding Circuit Set computation:

Choose an option: (type '?' for help) t

Set the number of strands: 6

Type a braid with 6 strands: ('6' = Delta)

3 2 1

Type the name of the output file: foo.txt

Error in MinCS.

Source files still mention GPLv2

Hi, it looks like the intention (a long time ago) was to switch to the GPLv3+ license. However, the headers of the individual files in the project still mention the GPLv2. If the goal is to adopt v3, then you should update those header comments so that someone can't take their code under the GPLv2.

ultra summit set segfaults

Bug uncovered by Bert Wiest.

--------------------------------------------------------
----------------  This is Braiding 1.0  ----------------
--------------------------------------------------------
-----|  Copyright (C) 2004 Juan Gonzalez-Meneses  |-----
-----| Braiding comes with ABSOLUTELY NO WARRANTY |-----
-----|           This is free software            |-----
-----| See GNU General Public License in GPL.txt  |-----
--------------------------------------------------------

l: Left Normal Form          r: Right Normal Form       

p: Permutation               x: Crossing numbers        

v: Least Common Multiple     ^: Greatest Common Divisor 

s: Super Summit Set          z: Centralizer             

e: Conjugacy Test            u: Ultra Summit Set        

t: Set of Sliding Circuits   a: Ask for Powers (On/Off)   

q: Quit             

--------------------------------------------------------

Choose an option: (type '?' for help) u

Set the number of strands: 6

Type a braid with 6 strands: ('6' = Delta)

2 1 3 2 1 4 3 2 5 4 3 2 1 1 4

Type the name of the output file: foo.txt

Segmentation fault (core dumped)

Randomize() for BandBraid is not correct.

Issue:

Randomization for band braids does not work, because of an error in BallotSequence (cbraid.cpp).
BallotSequence currently isn't injective, and may segfault.
This is caused by an off-by-one error in recursive calls to BallotSequence.

Suggested fix:

void BallotSequence(sint16 n, cln::cl_I k, sint8 *s) {
    sint16 i;
    cln::cl_I r;

    if (k <= (r = GetCatalanNumber(n - 1) * GetCatalanNumber(0)))
        i = 1;
    else if (k > (r = GetCatalanNumber(n) - r)) {
        i = n;
        k = k - r;
    }
    else {
        for (i = 1; i <= n; ++i) {
            if (k <= (r = GetCatalanNumber(i - 1) * GetCatalanNumber(n - i)))
                break;
            else
                k = k - r;
        }
    }

    cln::cl_I_div_t d = cln::floor2(k - 1, GetCatalanNumber(n - i));
    s[1] = 1;
    s[2 * i] = -1;
    if (i > 1)
        BallotSequence(i - 1, d.quotient + 1, s + 1);
    if (i < n)
        BallotSequence(n - i, d.remainder + 1, s + 2 * i);
}

Is this Linux only?

Hi there, is this project Linux only? I don't immediately see any releases.