/// <summary>
/// Construct packed versions of input matrices, and then use sparse row/column dot
/// to compute elements of output matrix. This is faster. But still relatively expensive.
/// </summary>
void multiply_fast(SymmetricSparseMatrix M2in, ref SymmetricSparseMatrix Rin, bool bParallel)
{
int N = Rows;
if (M2in.Rows != N)
{
throw new Exception("SymmetricSparseMatrix.Multiply: matrices have incompatible dimensions");
}
if (Rin == null)
{
Rin = new SymmetricSparseMatrix();
}
SymmetricSparseMatrix R = Rin; // require alias for use in lambda below
PackedSparseMatrix M = new PackedSparseMatrix(this);
M.Sort();
PackedSparseMatrix M2 = new PackedSparseMatrix(M2in, true);
M2.Sort();
// Parallel variant is vastly faster, uses spinlock to control access to R
if (bParallel)
{
// goddamn SpinLock is in .Net 4
//SpinLock spin = new SpinLock();
gParallel.ForEach(Interval1i.Range(N), (r1i) => {
for (int c2i = r1i; c2i < N; c2i++)
{
double v = M.DotRowColumn(r1i, c2i, M2);
if (Math.Abs(v) > math.MathUtil.ZeroTolerance)
{
//bool taken = false;
//spin.Enter(ref taken);
//Debug.Assert(taken);
//R[r1i, c2i] = v;
//spin.Exit();
lock (R) {
R[r1i, c2i] = v;
}
}
}
});
}
else
{
for (int r1i = 0; r1i < N; r1i++)
{
for (int c2i = r1i; c2i < N; c2i++)
{
double v = M.DotRowColumn(r1i, c2i, M2);
if (Math.Abs(v) > math.MathUtil.ZeroTolerance)
{
R[r1i, c2i] = v;
}
}
}
}
}
// returns this*this (requires less memory)
public SymmetricSparseMatrix Square(bool bParallel = true)
{
SymmetricSparseMatrix R = new SymmetricSparseMatrix();
PackedSparseMatrix M = new PackedSparseMatrix(this);
M.Sort();
// Parallel variant is vastly faster, uses spinlock to control access to R
if (bParallel)
{
// goddamn SpinLock is in .Net 4
//SpinLock spin = new SpinLock();
gParallel.ForEach(Interval1i.Range(N), (r1i) => {
for (int c2i = r1i; c2i < N; c2i++)
{
double v = M.DotRowColumn(r1i, c2i, M);
if (Math.Abs(v) > math.MathUtil.ZeroTolerance)
{
//bool taken = false;
//spin.Enter(ref taken);
//Debug.Assert(taken);
//R[r1i, c2i] = v;
//spin.Exit();
lock (R) {
R[r1i, c2i] = v;
}
}
}
});
}
else
{
for (int r1i = 0; r1i < N; r1i++)
{
for (int c2i = r1i; c2i < N; c2i++)
{
double v = M.DotRowColumn(r1i, c2i, M);
if (Math.Abs(v) > math.MathUtil.ZeroTolerance)
{
R[r1i, c2i] = v;
}
}
}
}
return(R);
}