On Fri, Apr 16, 2010 at 5:28 PM, Alec Mihailovs <[email protected]> wrote: > On Apr 16, 5:05 pm, David Joyner <[email protected]> wrote: > >> Do you mean A is the matrix of all n^k codewords, but you remove the >> columns corresponding to the erasure positions? I don't know what you >> mean by A. > > I meant the submatrix of G - I used something like that in the decode > procedure in another post, just replacing A.transpose() with a random > matrix. >
Perhaps I don't understand your program, but it appears to not address the issue. Here is the algorithm, if I understand the question correctly: Let I denote the subset of range(n) which represents the erasures. Let v denote the vector in GF(q)^n which you want to decode. Let C denote the [n,k,d] code with generator matrix G (so the rows of G are a basis for the vector space C over GF(q)). For each w in GF(q)^n, let w^I denote those coordinates of w not in I. Let L = [] be an empty list. For each c in C if c^I = v^I then append c to L return L This gives you the list of codewords desired. I don't see how the output of your programs agree with this. > I looked at the C.decode (for C in the original post), and it does > something different - it corrects the errors. Perhaps, the better name > for it would be C.correct ? > > Also, perhaps, just simple linsolve can be used (in my decode) if it > exists in Sage and works for overdetermined systems of linear > equations. > > Alec > > -- > To post to this group, send email to [email protected] > To unsubscribe from this group, send email to > [email protected] > For more options, visit this group at > http://groups.google.com/group/sage-support > URL: http://www.sagemath.org > -- To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
