# ummm, in retrospect…

Update: I had another look at this. Actually, in retrospect, the substance of the lecture notes are not wrong, but they are worded for electronic engineers rather than computer scientists or mathematicians

Normally one would present the process of creating a code word in the form:

$P(x) = m(x)G(x)$

Where $P(x)$ is the code word, $m(x)$ is the message to be coded and $G(x)$ the generator matrix. The lecture notes present the generator matrix in a systematic form which would be the equivalent of:

$P(x) = m(x)IG(x)$, where $I$ is the identity matrix.

Here’s a quandry: you are researching “Cyclic Redundancy Codes” (CRCs) – mainly for finding a clearer way to explain them, when you come across some lecture notes from an academic at one of the bigger universities in Western Europe which, initially at least, look like a model of clear exposition.

But as you read on, you realise with growing incredulity that what the lecturer describes as CRCs are not CRCs at all but general linear block codes.

Now, the principles are similar – in that the lecturer discusses generator matrices and parity check matrices, but the details are hopelessly wrong.

So, do you (a) denounce the academic in public, or (b) contact them in private or (c) post a ‘blind’ blog and wonder about what value students and taxpayers are getting for their money?

• prubin73 says:

I agree. If the response is unsatisfactory, then perhaps option (a) becomes the fallback.

• Having looked at this again I wonder if I am the one who has just got this wrong and, actually, the presentation is just clear than many other presentations
I might delete this post.

1. I am concerned now, though, that having said bad things about them here I’d be asking for trouble (legal and otherwise) if I went to them.

• prubin73 says:

Saying someone is incorrect should not incur any legal trouble. Also, you have not named them here (at least not yet). You can offer to update this post if either (a) it turns out they are correct and you are off base or (b) they realize they made an error and fix it online.