# Quantum Development Kit Toffoli Simulator

The Quantum Development Kit provides a Toffoli simulator, which is a special-purpose simulator that can simulate quantum algorithms that are limited to X, CNOT, and multi-controlled X quantum operations (all classical logic and computations are available).

While the Toffoli simulator is much more restricted in operation than the full state simulator, it can simulate far more qubits. The Toffoli simulator can be used with millions of qubits, while the full state simulator is generally limited to about 30. It can execute and debug a limited set of quantum algorithms written in Q# on your computer; for instance, oracles that evaluate Boolean functions can be implemented using these gates and so tested on vary large numbers of qubits using this simulator.

This quantum simulator is exposed via the ToffoliSimulator class. To use the simulator, simply create an instance of this class and pass it to the Run method of the quantum operation you want to execute along with the rest of the parameters:

    var sim = new ToffoliSimulator();
var res = myOperation.Run(sim).Result;
///...


## Other Operations

The ToffoliSimulator supports rotations and exponentiated Paulis, such as R and Exp, when the resulting operation is equal to X or to the identity.

Measurement and assert are supported, but only in the Pauli Z basis. Note that the probability of some measurement is always either 0 or 1; there is no randomness in the Toffoli simulator.

DumpMachine and DumpRegister are supported. They both output the current Z-basis state of each qubit, one qubit per line.

## QubitCount

By default, the ToffoliSimulator allocates space for 65,536 qubits. If your algorithm requires more than this, you can change the qubit count by providing a value for the qubitCount parameter to the constructor. Each additional qubit requires an additional byte of memory, so there is no significant cost to overestimating the number of qubits you'll need.

For example:

    var sim = new ToffoliSimulator(qubitCount: 1000000);
var res = myLargeOperation.Run(sim).Result;