update notations
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@@ -92,10 +92,10 @@ Two equivalent ways to constructing a linear code:
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- A **parity check** matrix $H\in \mathbb{F}^{(n-k)\times n}$ with $(n-k)$ rows and $n$ columns.
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$$
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\mathcal{C}=\{c\in \mathbb{F}^n:Hc^T=0\}
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\mathcal{C}=\{c\in \mathbb{F}^n:Hc^\top=0\}
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$$
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- The right kernel of $H$ is $\mathcal{C}$.
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- Multiplying $c^T$ by $H$ "checks" if $c\in \mathcal{C}$.
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- Multiplying $c^\top$ by $H$ "checks" if $c\in \mathcal{C}$.
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### Encoding of linear codes
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@@ -144,7 +144,7 @@ Decoding: $(y+e)\to x$, $y=xG$.
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Use **syndrome** to identify which coset $\mathcal{C}_i$ that the noisy-code to $\mathcal{C}_i+e$ belongs to.
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$$
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H(y+e)^T=H(y+e)=Hx+He=He
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H(y+e)^\top=H(y+e)=Hx+He=He
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$$
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### Syndrome decoding
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@@ -215,7 +215,7 @@ Fourth row is $\mathcal{C}+(00100)$.
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Any two elements in a row are of the form $y_1'=y_1+e$ and $y_2'=y_2+e$ for some $e\in \mathbb{F}^n$.
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Same syndrome if $H(y_1'+e)^T=H(y_2'+e)^T$.
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Same syndrome if $H(y_1'+e)^\top=H(y_2'+e)^\top$.
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Entries in different rows have different syndrome.
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