Working through a bioinformatics textbook currently, when I ran into this set of sigma equations:
$$\sum_jJ_{ij}S_j+h>0\to S_i(t+1)=1\\[5pt]\sum_jJ_{ij}S_j+h\le0\to S_i(t+1)=0$$
My interpretation of it is that it means if the sum from $j$ to $S_i(t+1)$ of $J_{ij}S_j + h$ is less than $0$, then the equation evaluates to a value of $1$. Similarly if it is less than or equal to $0$, it evaluates to $0$ (for the bottom one). Is that correct?
$p(x)\rightarrow q(x)$ is the logical operator if.
If p(x) is true, then q(x) is true
If p(x) is false, then q(x) is unknown(until you actually calculate it)
The logical operator iff(if and only if) is a stronger version of the operator if
$p(x)\leftrightarrow q(x)$ means
If and only if p(x) is true, q(x) is true