Template naming

This document is meant to clarify the intended usage of common template names found within qsim. The following table provides example types for each; note however that there may be other types which are also used for these templates, and users may define their own alternatives to the examples below so long as they fulfill the same expectations.

Name Example Type
Args (parfor.h) Arguments to a Function object.
Bitstring Alias for uint64_t.
Circuit Circuit
Container (util.h) A vector of strings, or Op's output type.
Ctype A complex type, e.g. std::complex<float>.
For for loop abstractions, see below.
ForArgs Arguments for constructing For objects, see below.
FP (simulator_basic.h) Same as fp_type.
fp_type A floating-point type, i.e. float or double.
Function (parfor.h) Any function; args are specified with Args.
FuserT BasicGateFuser
Gate Gate
GateCirq GateCirq
GateDef GateRX
GateQSim GateQSim
GK / GateKind GateKind
HybridSimulator HybridSimulator
IOFile IOFile
Matrix A numeric C++ vector representing a matrix.
MeasurementFunc measure (in PrintAmplitudes)
Op (util.h) to_int (in Options)
ParallelFor ParallelFor
Params Vector of fp_type.
SequentialFor SequentialFor
Simulator SimulatorAVX
State Unique pointer to fp_type.
StateSpace StateSpace
Stream A valid input for std::getline().

For and ForArgs

For type represents a for loop. It is a template parameter of the StateSpace* (lib/statespace.h) and Simulator* (lib/simulator.h) classes. For objects in these classes are utilized to iterate over quantum state arrays. ForArgs is a variadic template parameter pack of the constructors of StateSpace* and Simulator*. It is utilized to pass arguments to the constructors of For objects.

The qsim library provides ParallelFor (lib/parfor.h) and SequentialFor (lib/seqfor.h). The user can also use custom For types. Examples of usage follow.

// ParallelFor(unsigned num_threads) constructor
SimulatorAVX<ParallelFor> simulator(num_qubits, num_threads);
// copy constructor
ParallelFor parallel_for(num_threads);
SimulatorAVX<ParallelFor> simulator(num_qubits, parallel_for);
ParallelFor parallel_for(num_threads);
// const reference to parallel_for in simulator
SimulatorAVX<const ParallelFor&> simulator(num_qubits, parallel_for);

In the following, we assume a custom MyFor type that has MyFor(unsigned num_threads, const Context& context) and copy constructors.

// MyFor(unsigned num_threads, const Context& context) constructor
SimulatorAVX<MyFor> simulator(num_qubits, num_threads, context);
// copy constructor
MyFor my_for(num_threads, context);
SimulatorAVX<MyFor> simulator(num_qubits, my_for);
// const reference to my_for in simulator
MyFor my_for(num_threads, context);
SimulatorAVX<const MyFor&> simulator(num_qubits, my_for);

Historical note

For the most part, the usage of templates in qsim (as opposed to interfaces) is a stylistic choice oriented towards generic programming and policy-based design. However, there are a small set of cases (most notably in ParallelFor) where the use of templates provides a meaningful performance improvement over other design patterns.