Qiskit / qiskit / 36051775345

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Committed by web-flow

Commit Message

Add nodes to cast a dtype and broadcast a shape (#16934)

* Add ops to cast a dtype and broadcast a shape

Arithmetic promotes and broadcasts its own operands, so these two ops are
operations a caller may want rather than glue every op demands. `Cast` reaches a
dtype promotion would not choose, and `BroadcastTo` reaches a shape arithmetic
has no second operand to reach.

`BroadcastTo` right-aligns its operand against a target shape, so an axis of
size one grows to any size and leading axes may be added. An axis cannot be
dropped, since the result shape is the target. A bounded target axis means the
operand's axis is carried through, and is admitted only where the operand has
that same axis: nothing else supplies its size, and evaluation takes the size
from the operand.

`Cast` refuses a real target for a complex operand.

Their inference is two more entries in the per-family set,
`rules::broadcast_dims_to` is the type-level shape rule beside `broadcast_dims`,
and `Tensor::broadcast_to` is its value-level counterpart.

* Assert on error variants rather than on error messages

A test that reads an error's `Display` output has to change whenever the wording
does, and the errors these tests read no longer derive `PartialEq` either.

Coverage Stats

442 of 456 new or added lines in 6 files covered. (96.93%)

25 existing lines in 3 files now uncovered.

122355 of 138869 relevant lines covered (88.11%)

942857.27 hits per line