Source code for cirq.study.resolver

# Copyright 2018 The Cirq Developers
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Resolves ParameterValues to assigned values."""
import numbers
from typing import Any, Dict, Iterator, Optional, TYPE_CHECKING, Union, cast
import numpy as np
import sympy
from sympy.core import numbers as sympy_numbers
from cirq._compat import proper_repr
from cirq._doc import document

if TYPE_CHECKING:
    import cirq


ParamDictType = Dict['cirq.TParamKey', 'cirq.TParamVal']
document(
    ParamDictType,  # type: ignore
    """Dictionary from symbols to values.""")

ParamResolverOrSimilarType = Union['cirq.ParamResolver', ParamDictType, None]
document(
    ParamResolverOrSimilarType,  # type: ignore
    """Something that can be used to turn parameters into values.""")


[docs]class ParamResolver: """Resolves parameters to actual values. A parameter is a variable whose value has not been determined. A ParamResolver is an object that can be used to assign values for these variables. ParamResolvers are hashable. Attributes: param_dict: A dictionary from the ParameterValue key (str) to its assigned value. """ def __new__(cls, param_dict: 'cirq.ParamResolverOrSimilarType' = None): if isinstance(param_dict, ParamResolver): return param_dict return super().__new__(cls)
[docs] def __init__(self, param_dict: 'cirq.ParamResolverOrSimilarType' = None) -> None: if hasattr(self, 'param_dict'): return # Already initialized. Got wrapped as part of the __new__. self._param_hash: Optional[int] = None self.param_dict = cast(ParamDictType, {} if param_dict is None else param_dict)
[docs] def value_of(self, value: Union['cirq.TParamKey', float]) -> 'cirq.TParamVal': """Attempt to resolve a parameter to its assigned value. Floats are returned without modification. Strings are resolved via the parameter dictionary with exact match only. Otherwise, strings are considered to be sympy.Symbols with the name as the input string. A sympy.Symbol is first checked for exact match in the parameter dictionary. Otherwise, it is treated as a sympy.Basic. A sympy.Basic is resolved using sympy substitution. Note that passing a formula to this resolver can be slow due to the underlying sympy library. For circuits relying on quick performance, it is recommended that all formulas are flattened before-hand using cirq.flatten or other means so that formula resolution is avoided. If unable to resolve a sympy.Symbol, returns it unchanged. If unable to resolve a name, returns a sympy.Symbol with that name. Args: value: The parameter to try to resolve. Returns: The value of the parameter as resolved by this resolver. """ # Input is a pass through type, no resolution needed: return early v = _sympy_pass_through(value) if v is not None: return v # Handles 2 cases: # Input is a string and maps to a number in the dictionary # Input is a symbol and maps to a number in the dictionary # In both cases, return it directly. if value in self.param_dict: param_value = self.param_dict[value] v = _sympy_pass_through(param_value) if v is not None: return v # Input is a string and is not in the dictionary. # Treat it as a symbol instead. if isinstance(value, str): # If the string is in the param_dict as a value, return it. # Otherwise, try using the symbol instead. return self.value_of(sympy.Symbol(value)) # Input is a symbol (sympy.Symbol('a')) and its string maps to a number # in the dictionary ({'a': 1.0}). Return it. if isinstance(value, sympy.Symbol) and value.name in self.param_dict: param_value = self.param_dict[value.name] v = _sympy_pass_through(param_value) if v is not None: return v # The following resolves common sympy expressions # If sympy did its job and wasn't slower than molasses, # we wouldn't need the following block. if isinstance(value, sympy.Add): summation = self.value_of(value.args[0]) for addend in value.args[1:]: summation += self.value_of(addend) return summation if isinstance(value, sympy.Mul): product = self.value_of(value.args[0]) for factor in value.args[1:]: product *= self.value_of(factor) return product if isinstance(value, sympy.Pow) and len(value.args) == 2: return np.power(self.value_of(value.args[0]), self.value_of(value.args[1])) # Input is either a sympy formula or the dictionary maps to a # formula. Use sympy to resolve the value. # Note that sympy.subs() is slow, so we want to avoid this and # only use it for cases that require complicated resolution. if isinstance(value, sympy.Basic): v = value.subs(self.param_dict) if v.free_symbols: return v elif sympy.im(v): return complex(v) else: return float(v) # No known way to resolve this variable, return unchanged. return value
def __iter__(self) -> Iterator[Union[str, sympy.Symbol]]: return iter(self.param_dict) def __bool__(self) -> bool: return bool(self.param_dict) def __getitem__(self, key: Union[sympy.Basic, float, str]) -> 'cirq.TParamVal': return self.value_of(key) def __hash__(self) -> int: if self._param_hash is None: self._param_hash = hash(frozenset(self.param_dict.items())) return self._param_hash def __eq__(self, other): if not isinstance(other, ParamResolver): return NotImplemented return self.param_dict == other.param_dict def __ne__(self, other): return not self == other def __repr__(self) -> str: param_dict_repr = ('{' + ', '.join([ f'{proper_repr(k)}: {proper_repr(v)}' for k, v in self.param_dict.items() ]) + '}') return f'cirq.ParamResolver({param_dict_repr})' def _json_dict_(self) -> Dict[str, Any]: return { 'cirq_type': self.__class__.__name__, # JSON requires mappings to have keys of basic types. 'param_dict': list(self.param_dict.items()) } @classmethod def _from_json_dict_(cls, param_dict, **kwargs): return cls(dict(param_dict))
def _sympy_pass_through(val: Any) -> Optional[Any]: if isinstance(val, numbers.Number) and not isinstance(val, sympy.Basic): return val if isinstance(val, sympy_numbers.IntegerConstant): return val.p if isinstance(val, sympy_numbers.RationalConstant): return val.p / val.q if val == sympy.pi: return np.pi return None