int testMomentum(){
int n = 10;
int i;
double momentum[3];
int failed = 0;
particle * stuff = malloc(n * sizeof(particle));
initialize_linearx(stuff, n);
//zero momentum
totalMomentum(stuff, n, momentum);
if(momentum[0] != 0 || momentum[1] != 0 || momentum[2] != 0){
failed++;
printf("nonzero momentum found x=%lf y=%lf z=%lf, expected zero momentum\n", momentum[0], momentum[1], momentum[2]);
}
//some momentum expected
stuff[0].vx = 1;
stuff[1].vx = 2;
stuff[1].vy = 2;
totalMomentum(stuff, n, momentum);
if(momentum[0] != 3 || momentum[1] != 2 || momentum[2] != 0){
failed++;
printf("unexpected momentum found x=%lf y=%lf z=%lf, expected 3,2,0\n", momentum[0], momentum[1], momentum[2]);
}
//non-equal masses
stuff[0].mass = 2;
totalMomentum(stuff, n, momentum);
if(momentum[0] != 4 || momentum[1] != 2 || momentum[2] != 0){
failed++;
printf("unexpected momentum found x=%lf y=%lf z=%lf, expected 4,2,0\n", momentum[0], momentum[1], momentum[2]);
}
//fprintParticles(stdout, stuff, n);
free(stuff);
if(failed == 0){
printf("momentum calculation passed\n");
}
return !failed;
}
Vector3D* GrapheneLatticeCreator::createVelocities(double *T,
VelocityDistribution distribution, bool* fixingMap)
{
//defining random function
function<Vector3D()> next;
std::mt19937 *generator = NULL;
std::normal_distribution<double> *dist = NULL;
switch (distribution)
{
case MAXWELLBOLTZMANN:
dist = new std::normal_distribution<double>(0, 1);
generator = new std::mt19937((unsigned)time(0));
next = [generator, dist]() {
return Vector3D((*dist)(*generator), (*dist)(*generator), (*dist)(*generator));
};
break;
case UNIFORM:
default:
srand((unsigned int)time(0));
next = []() {
Vector3D v(
(double)rand() / RAND_MAX - 0.5,
(double)rand() / RAND_MAX - 0.5,
(double)rand() / RAND_MAX - 0.5
);
return v / v.norm();
};
break;
}
Vector3D* velocities = new Vector3D[l * w * c];
Vector3D totalMomentum(0, 0, 0);
unsigned movable = 0;
for (size_t i = 0; i < l; ++i)
{
for (size_t j = 0; j < w; ++j)
{
for (size_t k = 0; k < c; ++k)
{
size_t idx = linearize(i, j, k);
if (fixingMap[idx])
{
velocities[idx] = Vector3D(0, 0, 0);
}
else
{
velocities[idx] = next();
++movable;
totalMomentum = totalMomentum + velocities[idx];
}
}
}
}
totalMomentum = totalMomentum / (double)movable;
for (size_t i = 0; i < l; i++)
{
for (size_t j = 0; j < w; j++)
{
for (size_t k = 0; k < c; k++)
{
size_t idx = linearize(i, j, k);
if (!fixingMap[idx])
{
velocities[idx] = velocities[idx] - totalMomentum;
}
}
}
}
for (size_t i = 0; i < l; i++)
{
int number = 0;
double v2 = 0;
for (size_t j = 0; j < w; j++)
{
for (size_t k = 0; k < c; k++)
{
size_t idx = linearize(i, j, k);
if (!fixingMap[idx])
{
++number;
v2 += velocities[idx] || velocities[idx];
}
}
}
v2 *= a2m * a2m;
double multiplier = sqrt(3 * number * boltzmann * T[i] / mass / v2);
for (size_t j = 0; j < w; ++j)
{
for (size_t k = 0; k < c; ++k)
{
size_t idx = linearize(i, j, k);
velocities[idx] = multiplier * velocities[idx];
totalMomentum = totalMomentum + velocities[idx];
}
}
}
if (dist != NULL)
{
delete dist;
dist = NULL;
}
if (generator != NULL)
{
delete generator;
generator = NULL;
}
return velocities;
}
