THIS CODE IS GROSS

View a much more user-friendly yet more powerful library here.

Note also the Hessian method used here is incorrect; see utilities.c in this shorter repo for a correct implementation.

The below instructions are out of date, since the interface has become more flexible. See hamiltonian_builder.h for creating a Hamiltonian, and see the
/*
 * PERFORM SIMULATION
 */
section of variational_3SAT_solver.c to see an example of how to use param_evolver.h. Feel free to contact me (via the email address advertised at qtechtheory.org/tyson.jones) with questions and guidance.

Variational Imag-Time 3SAT Solver

Setup

You'll need to install the GNU Scientific library; instructions here.

The executable Variational3SATSolver has main in variational_3SAT_solver.c and includes

QuEST
sat_generator which generates the 3SAT problems :^)
hamiltonian_builder which builds the Hamiltonians :^)
param_evolver which evolves the parameters :^) with the variational imagianry time method
mmaformatter which formats the output for importing into Mathematica

The QuEST makefile must be adapted for GSL. The changes are outlined here and my makefile is included in this repo.

Running

THESE INSTRUCTIONS ARE OUT OF DATE: instead, run

./Variational3SATSolver help

OLD INSTRUCTIONS:

Variational3SATSolver accepts 9 command-line arguments:

num_bools: 3SAT problem size (a random instance will be generated)
num_params: the number of parameterised gates in the ansatz circuit
rseed: random seed for 3SAT generation
threshold: the probability of the solution state which when achieved, parameter evolution ends
timestep: multiplies the change the parameters experience at each imag-time evolution step. Passing 0 will use the smallest stable time-step, ~max(energyEigVal)
max_iters: maximum iterations to perform before halting (if not already converged to threshold)
wrap_params: whether (0 or 1) parameters will be wrapped-around to remain in [0, 2 PI) after each evolution step.
deriv_accuracy: order of finite difference deriv approx to use (1 to 4) in constructing A and C
matrix_noise: percent (0 to 1) noise to vary A and C elements by before solving for parameter evolution

Customising

The parameters are updated by the method

evolveOutcome evolveParams(
	evolverMemory *mem, 
	void (*ansatzCircuit)(MultiQubit, double*, int), 
	int (*inversionMethod)(evolverMemory*),
	MultiQubit qubits, 
	double* params, 
	Hamiltonian hamiltonian, 
	double timeStepSize, 
	int wrapParams
);

where ansatzCircuit and inversionMethod are functions you can define and pass, and mem is a data structure you must first create with

prepareEvolverMemory(MultiQubit qubits, int numParams);

ansatzCircuit must be a function which accepts a MultiQubit instance, the parameter list and its length, and applies an ansatz circuit for those parameter values to MultiQubit. It's important this ansatz circuit sets the initial state of the qubits. For example

void myAnsatz(MultiQubit qubits, double* params, int numParams) {
	
	initStateZero(&qubits);

	for (int p=0; p < numParams; p++)
		rotateX(qubits, p % qubits.numQubits, params[p]);
}

could be passed to evolveOutcome(..., myAnsatz, ...) In lieu of your own code, defaultAnsatzCircuit can be passed.

inversionMethod is called to numerically solve for the change in the parameters given the matrix equation. The function must modify mem->paramChange (which is a GSL vector) using the mem->matrA and mem->vecC matrix/vector, to generate a solution to matrA paramChange = vecC, and should return 1 if it also numerically fails.

In lieu of your own code, you can pass approxByLUDecomp, approxParamsByLeastSquares, approxParamsByRemovingVar, approxParamsByTSVD or approxParamsByTikhonov; see the code-doc in param_evolver.h for details. I recommend the latter, which ensures ||paramChange|| is small.

Underdetermined equations of paramChange can be realised by changing initStateZero to initStatePlus in defaultAnsatzCircuit.

hamiltonian must be an instance of Hamiltonian, declared in hamiltonian_builder.c, which you can construct via...

Hamiltonian getRandom3SATHamil(int numBools, int **equ, int **sol, int *numClauses);

to generate a random 3SAT equation and accompanying diagonal Hamiltonian, or...

Hamiltonian load3SATHamilFromFile(char *filename, int **equ, int **sol, int *numBools, int *numClauses);

to load a diagonal Hamiltonian from a 3SAT saved in a file, or...

Hamiltonian loadPauliHamilFromFile(char *filename);

to load a Hamiltonian specified as a sum of pauli matrix products, with format

coeff gateOnQubit1 gateOnQubit2 ... gateOnQubitN
coeff gateOnQubit1 gateOnQubit2 ... gateOnQubitN

where coeff is a double, gateOnQubitn is one of 0,1,2,3, signifying an I,X,Y,Z gate on that qubit.

Output

Variational3SATSolver (through variational_3SAT_solver.c) outputs a Mathematica association (using this) to file, which contains

expected energy over iterations
probability of the solution state over iterations
evolution of every parameter
which iterations underwent recovery numerical methods

and is simply read via

SetDirectory @ NotebookDirectory[];
data = Get["wickSATdata.txt"];