/// <summary>
/// Simulates on timestep of the time evolution by performing the splitstep fourier method only once.
/// </summary>
/// <param name="FT">Algorithm which will be used for the Fouriertransformation</param>
public void splitStepFourier(string FT)
{
int size = this.psi.Length;
// psi=psi.*exp(-0.5*1i*dt*(V+(g1d/hbar)*abs(psi).ˆ2));
for (int i = 0; i < size; i++)
{
psi[i] = psi[i] * ComplexNumber.Exp(-0.5 * ComplexNumber.ImaginaryOne * deltaT
* (V[i] + g1D / PhysConst.hbar
* Math.Pow(psi[i].Norm(), 2)));
}
// decides which algorithm will be used for the FT
switch (FT)
{
case "DFT":
psi = FFT.DFT(psi);
break;
case "CT":
psi = FFT.CT(psi);
break;
case "BR":
psi = FFT.BR(psi, reversedBits);
break;
default:
break;
}
psi = FFT.Shift(psi); // shift the lower half with the upper one to restore normal order
for (int i = 0; i < size; i++)
{
psi[i] = psi[i] / size;
}
// psi_k=psi_k*exp(-0.5*dt*1i*(hbar/m)*kˆ2)
for (int i = 0; i < size; i++)
{
psi[i] = psi[i] * ComplexNumber.Exp(-0.5 * ComplexNumber.ImaginaryOne * deltaT * PhysConst.hbar / mass * Math.Pow(K[i], 2));
}
psi = FFT.Shift(psi); // shifts again, so that the result of the IFT will be normal orderd
// decides which algorithm will be used for the IFT
switch (FT)
{
case "DFT":
psi = FFT.IDFT(psi);
break;
case "CT":
psi = FFT.ICT(psi);
break;
case "BR":
psi = FFT.IBR(psi, reversedBits);
break;
default:
break;
}
for (int i = 0; i < size; i++)
{
psi[i] = psi[i] * size;
}
//psi = psi.* exp(-0.5 * 1i * dt * (V + (g1d / hbar) * abs(psi).ˆ2));
for (int i = 0; i < size; i++)
{
psi[i] = psi[i] * ComplexNumber.Exp(-0.5 * ComplexNumber.ImaginaryOne * deltaT
* (V[i] + g1D / PhysConst.hbar
* Math.Pow(psi[i].Norm(), 2)));
}
}
/// <summary>
/// <c>getGroundState</c> deteremines the Groundstate of a the wavefunction saved in <c>this.psi</c>
/// with the imaginary time method
/// </summary>
public void getGroundState()
{
//ComplexNumber[] psi_0 = psi;
double mu = 1;
double mu_old;
double mu_error = 1;
ComplexNumber[] psi_old = new ComplexNumber[psi.Length];
double NormOfPsi = 0;
for (int i = 0; i < psi.Length; i++)
{
NormOfPsi += Math.Pow(psi[i].Norm(), 2);
}
NormOfPsi = Math.Sqrt(NormOfPsi) * deltaX;
int j = 0;
while (mu_error > Math.Pow(10, -8))
{
// creation of new wave function
psi_old = (ComplexNumber[])psi.Clone();
for (int i = 0; i < psi.Length; i++)
{
psi[i] = psi[i] * Math.Exp(-0.5 * deltaT * (V[i] + g1D / PhysConst.hbar * Math.Pow(psi[i].Norm(), 2)));
}
//ComplexNumber[] psi_k = new ComplexNumber[psi.Length];
psi = FFT.BR(psi, reversedBits); // Fourier transformation of the wave function with the Cooley-Tukey algorithm
psi = FFT.Shift(psi); //
for (int i = 0; i < psi.Length; i++)
{
psi[i] = psi[i] / xSteps;
}
// psi = psi*exp((-0.5*deltaT*hbar*|k|^2)/m)
for (int i = 0; i < psi.Length; i++)
{
psi[i] = psi[i] * Math.Exp(-0.5 * deltaT * (PhysConst.hbar / this.mass * Math.Pow(K[i], 2)));
}
psi = FFT.Shift(psi);
psi = FFT.IBR(psi, reversedBits); //Inverse fourier transformation of the wave function with the bit reverse algorithm
for (int i = 0; i < psi.Length; i++)
{
psi[i] = psi[i] * kSteps;
}
// psi = psi*exp(-0.5*deltaT*V(x)+g1D/hbar * |psi|^2)
for (int i = 0; i < psi.Length; i++)
{
psi[i] = psi[i] * Math.Exp(-0.5 * deltaT * (V[i] + g1D / PhysConst.hbar * Math.Pow(psi[i].Norm(), 2)));
}
mu_old = mu;
mu = Math.Log((psi_old[psi_old.Length / 2] / psi[psi.Length / 2]).Norm()) / deltaT;
mu_error = Math.Abs(mu - mu_old) / mu;
double currentNormOfPsi = 0;
for (int i = 0; i < psi.Length; i++)
{
currentNormOfPsi += Math.Pow(psi[i].Norm(), 2);
}
currentNormOfPsi = Math.Sqrt(currentNormOfPsi) * deltaX;
for (int i = 0; i < psi.Length; i++)
{
psi[i] = psi[i] * Math.Sqrt(NormOfPsi) / Math.Sqrt(currentNormOfPsi);
}
if (j > Math.Pow(10, 8))
{
break;
}
j++;
}
}
/// <summary>
/// Initializes a new instance of the <see cref="T:OurMaths.GPESolver"/> class
/// with basic definitions and external input.
/// </summary>
/// <param name="atomMass">Atom mass.</param>
/// <param name="numberOfAtoms">Number of atoms.</param>
/// <param name="scatteringlength">Scatteringlength.</param>
/// <param name="wx">Wx.</param>
/// <param name="wr">Wr.</param>
public GPESolver(double atomMass, int numberOfAtoms, double scatteringlength, double wx, double wr)
{
// Physical Defintion
mass = atomMass; // mass of an atom
aSc = scatteringlength; // Scattering Length
N = numberOfAtoms; // Atom number
wX = wx; // trap freq
lX = Math.Sqrt(PhysConst.hbar / (mass * wX)); //ho length of trap
wR = wr; // radial trap freq
lR = Math.Sqrt(PhysConst.hbar / (mass * wR)); // ho length of trap
g1D = 2 * Math.Pow(PhysConst.hbar, 2) * aSc / (mass * lR * lR); // 1D interaction coefficient
/// Grid definitions
xSteps = 512; // number of points im Ortsraum; power of two
kSteps = xSteps; // number of points in momentum space
deltaX = 2 * Math.Pow(10, -7); // distance between points im Ortsraum
deltaK = 2 * Math.PI / ((xSteps - 1) * deltaX); //distance between points in momentum space
deltaT = Math.Pow(10, -6); // time intervall
timeSteps = 10000; // Anzahl der Zeitentwicklungsschritte
// create Grids
X = new double[xSteps];
for (int i = 0; i < xSteps; i++)
{
X[i] = (i - xSteps / 2 + 1) * deltaX;
}
V = new double[xSteps];
for (int i = 0; i < xSteps; i++)
{
V[i] = 0.5 * mass * wX * wX * X[i] * X[i] / PhysConst.hbar;
}
K = new double[xSteps];
for (int i = 0; i < xSteps; i++)
{
K[i] = (i - xSteps / 2 + 1) * deltaK;
}
// prepare for bitReversal
reversedBits = new uint[xSteps];
int a = 0;
int findA = xSteps;
while (findA > 1)
{
findA = findA >> 1;
a++;
}
for (uint i = 0; i < xSteps; i++)
{
reversedBits[i] = FFT.BitReverse(i, a);
}
// create Starting wave function
psi = new ComplexNumber[xSteps];
for (int i = 0; i < xSteps; i++)
{
psi[i] = Math.Sqrt(N / lX) * Math.Pow(Math.PI, -0.25) * Math.Exp(-X[i] * X[i] / (2.2 * lX * lX));
}
}
