tfl.lattice_lib.project_by_dykstra

Applies dykstra's projection algorithm for monotonicity/trust constraints.

tfl.lattice_lib.project_by_dykstra(
    weights,
    lattice_sizes,
    monotonicities=None,
    unimodalities=None,
    edgeworth_trusts=None,
    trapezoid_trusts=None,
    monotonic_dominances=None,
    range_dominances=None,
    joint_monotonicities=None,
    joint_unimodalities=None,
    num_iterations=1
)

• Returns honest projection with respect to L2 norm if num_iterations is inf.
• Monotonicity will be violated by some small eps(num_iterations).
• Complexity: O(num_iterations * (num_monotonic_dims + num_trust_constraints)
  • num_lattice_weights)

Dykstra's alternating projections algorithm projects into intersection of several convex sets. For algorithm description itself use Google or Wiki: https://en.wikipedia.org/wiki/Dykstra%27s_projection_algorithm

Here, each monotonicity constraint is split up into 2 independent convex sets each trust constraint is split up into 4 independent convex sets. These sets are then projected onto exactly (in L2 space). For more details, see the _projectpartial* functions.

Args
weights	Lattice weights tensor of shape: (prod(lattice_sizes), units).
lattice_sizes	list or tuple of integers which represents lattice sizes. which correspond to weights.
monotonicities	None or list or tuple of same length as lattice_sizes of {0, 1} which represents monotonicity constraints per dimension. 1 stands for increasing (non-decreasing in fact), 0 for no monotonicity constraints.
unimodalities	None or list or tuple of same length as lattice_sizes of {-1, 0, 1} which represents unimodality constraints per dimension. 1 indicates that function first decreases then increases, -1 indicates that function first increases then decreases, 0 indicates no unimodality constraints.
edgeworth_trusts	None or iterable of three-element tuples. First element is the index of the main (monotonic) feature. Second element is the index of the conditional feature. Third element is the direction of trust: 1 if higher values of the conditional feature should increase trust in the main feature and -1 otherwise.
trapezoid_trusts	None or iterable of three-element tuples. First element is the index of the main (monotonic) feature. Second element is the index of the conditional feature. Third element is the direction of trust: 1 if higher values of the conditional feature should increase trust in the main feature and -1 otherwise.
monotonic_dominances	None or iterable of two-element tuples. First element is the index of the dominant feature. Second element is the index of the weak feature.
range_dominances	None or iterable of two-element tuples. First element is the index of the dominant feature. Second element is the index of the weak feature.
joint_monotonicities	None or iterable of two-element tuples. Each tuple represents a pair of feature indices that require joint monotoniticity.
joint_unimodalities	None or tuple or iterable of tuples. Each tuple represents indices of single group of jointly unimodal features followed by 'valley' or 'peak'.
num_iterations	number of iterations of Dykstra's algorithm.

Returns
Projected weights tensor of same shape as weights.