**Quantum Fog does NOT spend any memory
in saving transition amplitudes that equal zero. (By a zero amplitude we
really mean one whose magnitude is smaller than 10 ^{-12}). Thus,
a 1000 × 2000 transition matrix (for a node with 1000 states and 2000
input states) with a single non-zero entry occupies the same amount of memory
as a 1 × 1 non-zero transition matrix.**

It is possible to encounter situations in which the transition matrix of a node has so many columns or rows that there isn't enough memory to store it. If only a minority of the entries of such a matrix have a large magnitude, and the rest have a small one, one may wish to filter out those entries that have a small magnitude; that is, to replace them by zero so as to save memory.

Define GAP to be the smallest |A|, where A ranges over all *non-zero*
node amplitudes of every node of the graph. When you choose **Prune Node
Amplitudes...** from the **Prepare** menu, Quantum Fog first calculates
GAP. It then opens the following window:

This window displays the current value of GAP (rounded to the nearest power
of ten). Suppose you enter a number N in the shaded box to the right of the
words "I wish gap to be". If next you press the **OK** button, Quantum
Fog replaces by zero any amplitude whose magnitude is smaller than
10^{-N}. Obviously, this has no effect if 10^{-N} is smaller
than the initial GAP. This operation CAN'T BE UNDONE, so you better save
a duplicate copy of your file before trying this.