opt_einsum.paths.greedy

opt_einsum.paths.greedy(inputs, output, size_dict, memory_limit=None, choose_fn=None, cost_fn='memory-removed')[source]

Finds the path by a three stage algorithm:

  1. Eagerly compute Hadamard products.

  2. Greedily compute contractions to maximize removed_size

  3. Greedily compute outer products.

This algorithm scales quadratically with respect to the maximum number of elements sharing a common dim.

Parameters

  • inputs (list) – List of sets that represent the lhs side of the einsum subscript

  • output (set) – Set that represents the rhs side of the overall einsum subscript

  • size_dict (dictionary) – Dictionary of index sizes

  • memory_limit (int) – The maximum number of elements in a temporary array

  • choose_fn (callable, optional) – A function that chooses which contraction to perform from the queu

  • cost_fn (callable, optional) – A function that assigns a potential contraction a cost.

Returns

path – The contraction order (a list of tuples of ints).

Return type

list

Examples

>>> isets = [set('abd'), set('ac'), set('bdc')]
>>> oset = set('')
>>> idx_sizes = {'a': 1, 'b':2, 'c':3, 'd':4}
>>> greedy(isets, oset, idx_sizes)
[(0, 2), (0, 1)]