Talk:Low-density parity-check code: Difference between revisions

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:::: does "sqrt_d(k) ones per column" makes a matrix sparse?
::::: since sqrt(k)/k approaches 0 with k->infinity, I would say, yes, they are sparse... but that's just my opinion.
:::::: Are you sure that's right? By my working, we have for e.g. a 2D (square) code, there are <math>kd + (n-k) = dk + 2\sqrt{k}</math> ones in the parity-check matrix, and there are <math>n = k + 2\sqrt{k}</math> columns. From that, <math>\lim_{k\rightarrow \infty} \frac{dk + 2\sqrt{k}}{k + 2\sqrt{k}} = d</math>. Note that I'm tired, so I could easily have screwed up... [[User:Oli Filth|Oli Filth]]<sup>([[User talk:Oli Filth|talk]]<nowiki>|</nowiki>[[Special:Contributions/Oli_Filth|contribs]])</sup> 19:01, 8 June 2009 (UTC)
 
:::: I think that LDPC are also characterized by there ability to be efficiently decoded by a low complexity iterative decoding algorithm. [[User:Cunchem|Cunchem]] ([[User talk:Cunchem|talk]]) 14:54, 8 June 2009 (UTC)
::::: Not really. In the original Gallager codes you had to do a full matrix multiplication. The idea was just that there was algorithms doing this faster for sparse matrices than general algorithms, but it was definitely not low complexity.