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README.md initial LaTeX cleanup
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geky committed Oct 22, 2024
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Showing 1 changed file with 19 additions and 9 deletions.
28 changes: 19 additions & 9 deletions README.md
Original file line number Diff line number Diff line change
Expand Up @@ -115,27 +115,35 @@ If we want to correct $e$ byte-errors, we will need $n = 2e$ fixed
points. We can construct a generator polynomial $P(x)$ with $n$ fixed
points at $g^i$ where $i < n$ like so:

$$
$$ \\
P(x) = \prod_{i=0}^n \left(x - X_i\right)
$$

We could choose any arbitrary set of fixed points, but usually we choose
$g^i$ where $g$ is a [generator][generator] in GF(256), since it provides
a convenient mapping of integers to unique non-zero elements in GF(256).

Note that for any fixed point $g^i$, $x - g^i = g^i - g^i = 0$. And
since multiplying anything by zero is zero, this will make our entire
Note that for any fixed point $g^i$:

$$ \\
\begin{aligned}
x - g^i &= g^i - g^i \\
&= 0
\end{aligned}
$$

And since multiplying anything by zero is zero, this will make our entire
product zero. So for any fixed point $g^i$, $P(g^i)$ should also evaluate
to zero:

$$
$$ \\
P(g^i) = 0
$$

This gets real nifty when you look at the definition of our Reed-Solomon
code for codeword $C(x)$ given a message $M(x)$:

$$
$$ \\
C(x) = M(x) x^n - (M(x) x^n \bmod P(x))
$$

Expand All @@ -144,7 +152,7 @@ gives us a polynomial that is a multiple of $P(x)$. And since multiplying
anything by zero is zero, for any fixed point $g^i$, $C(g^i)$ should also
evaluate to zero:

$$
$$ \\
C(g^i) = 0
$$

Expand All @@ -163,9 +171,11 @@ $$
Check out what happens if we plug in our fixed point, $g^i$:

$$
C'(g^i) = C(g^i) + E(g^i)
= 0 + E(g^i)
= E(g^i)
\begin{aligned}
C'(g^i) &= C(g^i) + E(g^i) \\
&= 0 + E(g^i) \\
&= E(g^i)
\end{aligned}
$$

The original codeword drops out! Leaving us with an equation defined only
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