/*
* void UpdateBackwardMethod(double h)
*
* Backward method on velocity
* Trapezoidal method on position
*/
public void UpdateBackwardMethod(double h)
{
if (validCount <= 0)
{
return;
}
int[] validIndex = new int[validCount];
int indexTmp = 0;
for (int i = 0; i < maxStarNum; i++)
{
if (validMap[i] == true)
{
validIndex[indexTmp] = i;
indexTmp++;
}
}
VEC[] velAll = new VEC[validCount];
VEC[] new_velAll = new VEC[validCount];
VEC[] posAll = new VEC[validCount];
VEC[] new_posAll = new VEC[validCount];
VEC massAll = new VEC(validCount);
for (int i = 0; i < validCount; i++)
{
velAll[i] = new VEC(s[validIndex[i]].vel);
new_velAll[i] = new VEC(s[validIndex[i]].vel);
posAll[i] = new VEC(s[validIndex[i]].pos);
new_posAll[i] = new VEC(s[validIndex[i]].pos);
massAll[i] = s[validIndex[i]].mass;
}
double e_threshold = 1E-7;
double err = 1.0 + e_threshold;
int maxIterNum = 100;
while (err > e_threshold & maxIterNum > 0)
{
VECV3 F = new VECV3(2 * validCount);
for (int i = 0; i < validCount; i++)
{
VEC a = new VEC(3);
for (int j = 0; j < validCount; j++)
{
if (i != j)
{
a += VEC.Normalize(new_posAll[j] - new_posAll[i]) * massAll[j] / DistancePow2(new_posAll[i], new_posAll[j]);
}
}
F[i] = G * a - (new_velAll[i] - velAll[i]) / h;
}
for (int i = validCount; i < 2 * validCount; i++)
{
F[i] = (new_posAll[i - validCount] - posAll[i - validCount]) / h - 0.5 * (new_velAll[i - validCount] + velAll[i - validCount]);
}
MATM3 JF = new MATM3(2 * validCount);
MAT tmp;
for (int i = 0; i < validCount; i++)
{
tmp = new MAT(3);
for (int k = 0; k < 3; k++)
{
tmp[k][k] = -1.0 / h;
}
JF[i][i] = tmp;
}
for (int i = 0; i < validCount; i++)
{
for (int j_inJF = validCount; j_inJF < 2 * validCount; j_inJF++)
{
int j = j_inJF - validCount;
tmp = new MAT(3);
if (i != j)
{
for (int a = 0; a < 3; a++)
{
for (int b = 0; b < 3; b++)
{
if (a == b)
{
tmp[a][b] = massAll[j] * G *
(-3 * Math.Pow(DistancePow2(new_posAll[j], new_posAll[i]), -2.5) * (new_posAll[j][a] - new_posAll[i][a]) * new_posAll[j][a]
+ Math.Pow(DistancePow2(new_posAll[j], new_posAll[i]), -1.5));
}
else
{
tmp[a][b] = massAll[j] * G * -3 * Math.Pow(DistancePow2(new_posAll[j], new_posAll[i]), -2.5) * (new_posAll[j][a] - new_posAll[i][a]) * (new_posAll[j][b] - new_posAll[i][b]);
}
}
}
}
else
{
for (int a = 0; a < 3; a++)
{
for (int b = 0; b < 3; b++)
{
if (a == b)
{
double sInTmp = 0;
for (int k = 0; k < validCount; k++)
{
if (k != j)
{
sInTmp += massAll[k] *
(3 * Math.Pow(DistancePow2(new_posAll[k], new_posAll[j]), -2.5) * (new_posAll[k][a] - new_posAll[j][a]) * (new_posAll[k][a] - new_posAll[i][a])
- Math.Pow(DistancePow2(new_posAll[k], new_posAll[j]), -1.5));
}
}
tmp[a][a] = G * sInTmp;
}
else
{
double sInTmp = 0;
for (int k = 0; k < validCount; k++)
{
if (k != j)
{
sInTmp += massAll[k] *
(3 * Math.Pow(DistancePow2(new_posAll[k], new_posAll[j]), -2.5) * (new_posAll[k][a] - new_posAll[j][a]) * (new_posAll[k][b] * new_posAll[i][b]));
}
}
tmp[a][a] = G * sInTmp;
}
}
}
}
JF[i][j_inJF] = tmp;
}
}
for (int i = validCount; i < 2 * validCount; i++)
{
for (int j = 0; j < validCount; j++)
{
if (i - validCount == j)
{
tmp = new MAT(3);
for (int k = 0; k < 3; k++)
{
tmp[k][k] = -0.5;
}
JF[i][j] = tmp;
}
}
}
for (int i = validCount; i < 2 * validCount; i++)
{
for (int j = validCount; j < 2 * validCount; j++)
{
if (i == j)
{
tmp = new MAT(3);
for (int k = 0; k < 3; k++)
{
tmp[k][k] = 1.0 / h;
}
JF[i][j] = tmp;
}
}
}
VECV3 delta = numericalFunctions.LU_Solve(JF, -F);
for (int i = 0; i < validCount; i++)
{
new_velAll[i] += delta[i];
new_posAll[i] += delta[i + validCount];
}
err = VECV3.L2_norm_special(F);
maxIterNum--;
if (maxIterNum == 0)
{
Debug.Log("Max iter number reached. Err: " + err + " Using Forward method instead in this period.");
UpdateForwardMethod(h / 2.0);
UpdateForwardMethod(h / 2.0);
return;
}
}
for (int i = 0; i < validCount; i++)
{
if (maxIterNum != 0)
{
s[validIndex[i]].vel = new_velAll[i];
s[validIndex[i]].pos = new_posAll[i];
}
}
for (int i = 0; i < validCount; i++)
{
for (int j = i + 1; j < validCount; j++)
{
if (DistanceBetweenStarsPow2(s[validIndex[i]], s[validIndex[j]]) < minDistanceToDistroy)
{
s[validIndex[j]].pos += (s[validIndex[i]].pos - s[validIndex[j]].pos) * s[validIndex[i]].mass / (s[validIndex[j]].mass + s[validIndex[i]].mass);
s[validIndex[j]].vel = (s[validIndex[j]].vel * s[validIndex[j]].mass + s[validIndex[i]].vel * s[validIndex[i]].mass) / (s[validIndex[j]].mass + s[validIndex[i]].mass);
s[validIndex[j]].mass += s[validIndex[i]].mass;
DestroyStar(s[validIndex[i]], 0);
continue;
}
}
}
}
/*
* void UpdateTrapezoidalMethod(double h)
*
* Trapezoidal method on velocity
* Trapezoidal method on position
*
* Is the most accurate method
*/
public void UpdateTrapezoidalMethod(double h)
{
if (validCount <= 0)
{
return;
}
// Map valid star index into validIndex
int[] validIndex = new int[validCount];
int indexTmp = 0;
for (int i = 0; i < maxStarNum; i++)
{
if (validMap[i] == true)
{
validIndex[indexTmp] = i;
indexTmp++;
}
}
// copy velocity and position of all stars into arrays
VEC[] velAll = new VEC[validCount];
VEC[] new_velAll = new VEC[validCount];
VEC[] posAll = new VEC[validCount];
VEC[] new_posAll = new VEC[validCount];
VEC massAll = new VEC(validCount);
for (int i = 0; i < validCount; i++)
{
velAll[i] = new VEC(s[validIndex[i]].vel);
new_velAll[i] = new VEC(s[validIndex[i]].vel);
posAll[i] = new VEC(s[validIndex[i]].pos);
new_posAll[i] = new VEC(s[validIndex[i]].pos);
massAll[i] = s[validIndex[i]].mass;
}
double e_threshold = 1E-9; // the error threshold of performing Newton’s Method
double err = 1.0 + e_threshold;
int maxIterNum = 100; // Newton’s Method might not converge, we need a max iteration number to terminate.
while (err > e_threshold & maxIterNum > 0)
{
VECV3 F = new VECV3(2 * validCount);
for (int i = 0; i < validCount; i++)
{
VEC a = new VEC(3);
for (int j = 0; j < validCount; j++)
{
if (i != j)
{
a += 0.5 * VEC.Normalize(new_posAll[j] - new_posAll[i]) * massAll[j] / DistancePow2(new_posAll[i], new_posAll[j])
+ 0.5 * VEC.Normalize(posAll[j] - posAll[i]) * massAll[j] / DistancePow2(posAll[i], posAll[j]);
}
}
F[i] = G * a - (new_velAll[i] - velAll[i]) / h;
}
for (int i = validCount; i < 2 * validCount; i++)
{
F[i] = (new_posAll[i - validCount] - posAll[i - validCount]) / h - 0.5 * (new_velAll[i - validCount] + velAll[i - validCount]);
}
MATM3 JF = new MATM3(2 * validCount);
MAT tmp;
for (int i = 0; i < validCount; i++)
{
tmp = new MAT(3);
for (int k = 0; k < 3; k++)
{
tmp[k][k] = -1.0 / h;
}
JF[i][i] = tmp;
}
for (int i = 0; i < validCount; i++)
{
for (int j_inJF = validCount; j_inJF < 2 * validCount; j_inJF++)
{
int j = j_inJF - validCount;
tmp = new MAT(3);
if (i != j)
{
for (int a = 0; a < 3; a++)
{
for (int b = 0; b < 3; b++)
{
if (a == b)
{
tmp[a][b] = massAll[j] * G *
(-3 * Math.Pow(DistancePow2(new_posAll[j], new_posAll[i]), -2.5) * (new_posAll[j][a] - new_posAll[i][a]) * new_posAll[j][a]
+ Math.Pow(DistancePow2(new_posAll[j], new_posAll[i]), -1.5));
}
else
{
tmp[a][b] = massAll[j] * G * -3 * Math.Pow(DistancePow2(new_posAll[j], new_posAll[i]), -2.5) * (new_posAll[j][a] - new_posAll[i][a]) * (new_posAll[j][b] - new_posAll[i][b]);
}
}
}
}
else
{
for (int a = 0; a < 3; a++)
{
for (int b = 0; b < 3; b++)
{
if (a == b)
{
double sInTmp = 0;
for (int k = 0; k < validCount; k++)
{
if (k != j)
{
sInTmp += massAll[k] *
(3 * Math.Pow(DistancePow2(new_posAll[k], new_posAll[j]), -2.5) * (new_posAll[k][a] - new_posAll[j][a]) * (new_posAll[k][a] - new_posAll[i][a])
- Math.Pow(DistancePow2(new_posAll[k], new_posAll[j]), -1.5));
}
}
tmp[a][a] = G * sInTmp;
}
else
{
double sInTmp = 0;
for (int k = 0; k < validCount; k++)
{
if (k != j)
{
sInTmp += massAll[k] *
(3 * Math.Pow(DistancePow2(new_posAll[k], new_posAll[j]), -2.5) * (new_posAll[k][a] - new_posAll[j][a]) * (new_posAll[k][b] * new_posAll[i][b]));
}
}
tmp[a][a] = G * sInTmp;
}
}
}
}
JF[i][j_inJF] = 0.5 * tmp;
}
}
for (int i = validCount; i < 2 * validCount; i++)
{
for (int j = 0; j < validCount; j++)
{
if (i - validCount == j)
{
tmp = new MAT(3);
for (int k = 0; k < 3; k++)
{
tmp[k][k] = -0.5;
}
JF[i][j] = tmp;
}
}
}
for (int i = validCount; i < 2 * validCount; i++)
{
for (int j = validCount; j < 2 * validCount; j++)
{
if (i == j)
{
tmp = new MAT(3);
for (int k = 0; k < 3; k++)
{
tmp[k][k] = 1.0 / h;
}
JF[i][j] = tmp;
}
}
}
VECV3 delta = numericalFunctions.LU_Solve(JF, -F);
for (int i = 0; i < validCount; i++)
{
new_velAll[i] += delta[i];
new_posAll[i] += delta[i + validCount];
}
err = VECV3.L2_norm_special(F);
maxIterNum--;
if (maxIterNum == 0)
{
Debug.Log("Max iter number reached. Err: " + err + " Using Forward method instead in this period.");
for (int i = 0; i < numOfForwardMethodInstead; i++)
{
UpdateForwardMethod(h / numOfForwardMethodInstead);
}
return;
}
}
// Apply new position and velocity to Star objects
for (int i = 0; i < validCount; i++)
{
if (maxIterNum != 0)
{
s[validIndex[i]].vel = new_velAll[i];
s[validIndex[i]].pos = new_posAll[i];
}
}
// Check if any pair of stars have distance smaller than minDistanceToDistroy.
// If so, merge two stars.
for (int i = 0; i < validCount; i++)
{
for (int j = i + 1; j < validCount; j++)
{
if (DistanceBetweenStarsPow2(s[validIndex[i]], s[validIndex[j]]) < minDistanceToDistroy)
{
s[validIndex[j]].pos += (s[validIndex[i]].pos - s[validIndex[j]].pos) * s[validIndex[i]].mass / (s[validIndex[j]].mass + s[validIndex[i]].mass);
s[validIndex[j]].vel = (s[validIndex[j]].vel * s[validIndex[j]].mass + s[validIndex[i]].vel * s[validIndex[i]].mass) / (s[validIndex[j]].mass + s[validIndex[i]].mass);
s[validIndex[j]].mass += s[validIndex[i]].mass;
DestroyStar(s[validIndex[i]], 0);
continue;
}
}
}
}