Greedy optimizer

Greedy(; metric = removedsize, choose = pop!)

Greedy contraction path solver. Greedily selects contractions that maximize a metric.

Keywords

• metric is a function that evaluates candidate pairwise tensor contractions. Defaults to removedsize.
• choose is a function that extracts a pairwise tensor contraction between candidates. Defaults to candidate that maximize metric using pop!.
• outer If true, consider outer products as candidates. Defaults to false.

Implementation

The implementation uses a binary heaptree to sort candidate pairwise tensor contractions. Then recursively,

1. Selects and extracts a candidate from the heaptree using the choose function.
2. Updates the metric of the candidates which contain neighbouring indices to the one selected.
3. Append the selected index to the path and go back to step 1.