/// <summary>
/// Symbolic ordering and analysis for QR.
/// </summary>
/// <param name="A">Matrix to factorize.</param>
/// <param name="p">Permutation.</param>
protected void SymbolicAnalysis(CompressedColumnStorage <T> A, int[] p, bool natural)
{
int m = A.RowCount;
int n = A.ColumnCount;
var sym = this.S = new SymbolicFactorization();
// Fill-reducing ordering
sym.q = p;
var C = natural ? SymbolicColumnStorage.Create(A) : Permute(A, null, sym.q);
// etree of C'*C, where C=A(:,q)
sym.parent = GraphHelper.EliminationTree(m, n, C.ColumnPointers, C.RowIndices, true);
int[] post = GraphHelper.TreePostorder(sym.parent, n);
sym.cp = GraphHelper.ColumnCounts(C, sym.parent, post, true); // col counts chol(C'*C)
bool ok = C != null && sym.parent != null && sym.cp != null && CountV(C, sym);
if (ok)
{
sym.unz = 0;
for (int k = 0; k < n; k++)
{
sym.unz += sym.cp[k];
}
}
}
/// <summary>
/// Permutes a sparse matrix, C = PAQ.
/// </summary>
/// <param name="A">m-by-n, column-compressed matrix</param>
/// <param name="pinv">a permutation vector of length m</param>
/// <param name="q">a permutation vector of length n</param>
/// <returns>C = PAQ, null on error</returns>
private SymbolicColumnStorage Permute(CompressedColumnStorage <T> A, int[] pinv, int[] q)
{
int t, j, k, nz = 0;
int m = A.RowCount;
int n = A.ColumnCount;
var ap = A.ColumnPointers;
var ai = A.RowIndices;
var result = SymbolicColumnStorage.Create(A);
var cp = result.ColumnPointers;
var ci = result.RowIndices;
for (k = 0; k < n; k++)
{
// Column k of C is column q[k] of A
cp[k] = nz;
j = q != null ? (q[k]) : k;
for (t = ap[j]; t < ap[j + 1]; t++)
{
// Row i of A is row pinv[i] of C
ci[nz++] = pinv != null ? (pinv[ai[t]]) : ai[t];
}
}
// Finalize the last column of C
cp[n] = nz;
return(result);
}
/// <summary>
/// Symbolic ordering and analysis for QR.
/// </summary>
private void SymbolicAnalysis(ColumnOrdering order, CompressedColumnStorage <double> A)
{
int m = A.RowCount;
int n = A.ColumnCount;
var sym = this.symFactor = new SymbolicFactorization();
// Fill-reducing ordering
sym.q = AMD.Generate(A, order);
var C = order > 0 ? Permute(A, null, sym.q) : SymbolicColumnStorage.Create(A);
// etree of C'*C, where C=A(:,q)
sym.parent = GraphHelper.EliminationTree(m, n, C.ColumnPointers, C.RowIndices, true);
int[] post = GraphHelper.TreePostorder(sym.parent, n);
sym.cp = GraphHelper.ColumnCounts(C, sym.parent, post, true); // col counts chol(C'*C)
bool ok = C != null && sym.parent != null && sym.cp != null && CountV(C);
if (ok)
{
sym.unz = 0;
for (int k = 0; k < n; k++)
{
sym.unz += sym.cp[k];
}
}
}
/// <summary>
/// Ordering and symbolic analysis for a Cholesky factorization.
/// </summary>
/// <param name="A">Matrix to factorize.</param>
/// <param name="p">Permutation.</param>
private void SymbolicAnalysis(CompressedColumnStorage <Complex> A, int[] p)
{
int n = A.ColumnCount;
var sym = this.S = new SymbolicFactorization();
// Find inverse permutation.
sym.pinv = Permutation.Invert(p);
// C = spones(triu(A(P,P)))
var C = PermuteSym(A, sym.pinv, false);
// Find etree of C.
sym.parent = GraphHelper.EliminationTree(n, n, C.ColumnPointers, C.RowIndices, false);
// Postorder the etree.
var post = GraphHelper.TreePostorder(sym.parent, n);
// Find column counts of chol(C)
var c = GraphHelper.ColumnCounts(SymbolicColumnStorage.Create(C, false), sym.parent, post, false);
sym.cp = new int[n + 1];
// Find column pointers for L
sym.unz = sym.lnz = Helper.CumulativeSum(sym.cp, c, n);
}
/// <summary>
/// Compute the Numeric Cholesky factorization, L = chol (A, [pinv parent cp]).
/// </summary>
/// <returns>Numeric Cholesky factorization</returns>
private void Factorize(CompressedColumnStorage <Complex> A, IProgress <double> progress)
{
Complex d, lki;
int top, i, p, k, cci;
int n = A.ColumnCount;
// Allocate workspace.
var c = new int[n];
var s = new int[n];
var x = this.temp;
var colp = S.cp;
var pinv = S.pinv;
var parent = S.parent;
var C = pinv != null?PermuteSym(A, pinv, true) : A;
var cp = C.ColumnPointers;
var ci = C.RowIndices;
var cx = C.Values;
this.L = CompressedColumnStorage <Complex> .Create(n, n, colp[n]);
var lp = L.ColumnPointers;
var li = L.RowIndices;
var lx = L.Values;
for (k = 0; k < n; k++)
{
lp[k] = c[k] = colp[k];
}
double current = 0.0;
double step = n / 100.0;
for (k = 0; k < n; k++) // compute L(k,:) for L*L' = C
{
// Progress reporting.
if (k >= current)
{
current += step;
if (progress != null)
{
progress.Report(k / (double)n);
}
}
// Find nonzero pattern of L(k,:)
top = GraphHelper.EtreeReach(SymbolicColumnStorage.Create(C, false), k, parent, s, c);
x[k] = 0; // x (0:k) is now zero
for (p = cp[k]; p < cp[k + 1]; p++) // x = full(triu(C(:,k)))
{
if (ci[p] <= k)
{
x[ci[p]] = cx[p];
}
}
d = x[k]; // d = C(k,k)
x[k] = 0; // clear x for k+1st iteration
// Triangular solve
for (; top < n; top++) // solve L(0:k-1,0:k-1) * x = C(:,k)
{
i = s[top]; // s [top..n-1] is pattern of L(k,:)
lki = x[i] / lx[lp[i]]; // L(k,i) = x (i) / L(i,i)
x[i] = 0; // clear x for k+1st iteration
cci = c[i];
for (p = lp[i] + 1; p < cci; p++)
{
x[li[p]] -= lx[p] * lki;
}
d -= lki * Complex.Conjugate(lki); // d = d - L(k,i)*L(k,i)
p = c[i]++;
li[p] = k; // store L(k,i) in column i
lx[p] = Complex.Conjugate(lki);
}
// Compute L(k,k)
if (d.Real <= 0 || d.Imaginary != 0)
{
throw new Exception(Resources.MatrixSymmetricPositiveDefinite);
}
p = c[k]++;
li[p] = k; // store L(k,k) = sqrt (d) in column k
lx[p] = Complex.Sqrt(d);
}
lp[n] = colp[n]; // finalize L
}
/// <summary>
/// Compute the Numeric Cholesky factorization, L = chol (A, [pinv parent cp]).
/// </summary>
/// <returns>Numeric Cholesky factorization</returns>
private void Factorize(CompressedColumnStorage <double> A)
{
double d, lki;
int top, i, p, k;
int n = A.ColumnCount;
// Allocate workspace.
var c = new int[n];
var s = new int[n];
var x = new double[n];
var colp = symFactor.cp;
var pinv = symFactor.pinv;
var parent = symFactor.parent;
var C = pinv != null?PermuteSym(A, pinv, true) : A;
var cp = C.ColumnPointers;
var ci = C.RowIndices;
var cx = C.Values;
this.L = CompressedColumnStorage <double> .Create(n, n, colp[n]);
var lp = L.ColumnPointers;
var li = L.RowIndices;
var lx = L.Values;
//var lst = new List<int>();
var percent = 0;
for (k = 0; k < n; k++)
{
lp[k] = c[k] = colp[k];
}
for (k = 0; k < n; k++) // compute L(k,:) for L*L' = C
{
if (100 * k / n != percent)
{
Progress = percent = (100 * k) / n;
//Console.WriteLine("{0}% solve", percent);
}
// Find nonzero pattern of L(k,:)
top = GraphHelper.EtreeReach(SymbolicColumnStorage.Create(C, false), k, parent, s, c);
x[k] = 0; // x (0:k) is now zero
var tmp = cp[k + 1];
for (p = cp[k]; p < tmp; p++) // x = full(triu(C(:,k)))
{
if (ci[p] <= k)
{
x[ci[p]] = cx[p];
}
}
d = x[k]; // d = C(k,k)
x[k] = 0; // clear x for k+1st iteration
// Triangular solve
for (; top < n; top++) // solve L(0:k-1,0:k-1) * x = C(:,k)
{
i = s[top]; // s [top..n-1] is pattern of L(k,:)
lki = x[i] / lx[lp[i]]; // L(k,i) = x (i) / L(i,i)
x[i] = 0; // clear x for k+1st iteration
p = lp[i] + 1;
var cci = c[i];
for (p = lp[i] + 1; p < cci; p++)
{
x[li[p]] -= lx[p] * lki;
}
d -= lki * lki; // d = d - L(k,i)*L(k,i)
p = c[i]++;
li[p] = k; // store L(k,i) in column i
lx[p] = lki;
}
// Compute L(k,k)
if (d <= 0)
{
throw new NotPositiveDefiniteException("not pos def"); // TODO: ex
}
p = c[k]++;
li[p] = k; // store L(k,k) = sqrt (d) in column k
lx[p] = Math.Sqrt(d);
}
lp[n] = colp[n]; // finalize L
}
/// <summary>
/// Compute coarse and then fine Dulmage-Mendelsohn decomposition. seed
/// optionally selects a randomized algorithm.
/// </summary>
/// <param name="matrix">column-compressed matrix</param>
/// <param name="seed">0: natural, -1: reverse, random order otherwise</param>
/// <returns>Dulmage-Mendelsohn analysis</returns>
public static DulmageMendelsohn Generate <T>(CompressedColumnStorage <T> matrix, int seed = 0)
where T : struct, IEquatable <T>, IFormattable
{
int i, j, k, cnz, nc, nb1, nb2;
int[] Cp, ps, rs;
bool ok;
// We are not interested in the actual matrix values.
var A = SymbolicColumnStorage.Create(matrix);
// Maximum matching
int m = A.RowCount;
int n = A.ColumnCount;
var result = new DulmageMendelsohn(m, n); // allocate result
int[] p = result.p;
int[] q = result.q;
int[] r = result.r;
int[] s = result.s;
int[] cc = result.cc;
int[] rr = result.rr;
int[] jimatch = MaximumMatching.Generate(A, seed); // max transversal
if (jimatch == null)
{
return(null);
}
// Coarse decomposition
for (j = 0; j < n; j++)
{
s[j] = -1; // unmark all cols for bfs
}
for (i = 0; i < m; i++)
{
r[i] = -1; // unmark all rows for bfs
}
result.BreadthFirstSearch(A, n, r, s, q, jimatch, m, 0, 1); // find C1, R1 from C0*/
ok = result.BreadthFirstSearch(A, m, s, r, p, jimatch, 0, m, 3); // find R3, C3 from R0*/
if (!ok)
{
return(null);
}
result.Unmatched(n, s, q, cc, 0); // unmatched set C0
result.Matched(n, s, jimatch, m, p, q, cc, rr, 1, 1); // set R1 and C1
result.Matched(n, s, jimatch, m, p, q, cc, rr, 2, -1); // set R2 and C2
result.Matched(n, s, jimatch, m, p, q, cc, rr, 3, 3); // set R3 and C3
result.Unmatched(m, r, p, rr, 3); // unmatched set R0
// Fine decomposition
int[] pinv = Permutation.Invert(p); // pinv=p'
var C = SymbolicColumnStorage.Create(matrix);
A.Permute(pinv, q, C); // C=A(p,q) (it will hold A(R2,C2))
Cp = C.ColumnPointers;
nc = cc[3] - cc[2]; // delete cols C0, C1, and C3 from C
if (cc[2] > 0)
{
for (j = cc[2]; j <= cc[3]; j++)
{
Cp[j - cc[2]] = Cp[j];
}
}
C.Reshape(-1, nc);
if (rr[2] - rr[1] < m) // delete rows R0, R1, and R3 from C
{
RowPrune(C, nc, rr);
cnz = Cp[nc];
int[] Ci = C.RowIndices;
if (rr[1] > 0)
{
for (k = 0; k < cnz; k++)
{
Ci[k] -= rr[1];
}
}
}
C.Reshape(nc, -1);
var scc = FindScc(C, nc); // find strongly connected components of C*/
// Combine coarse and fine decompositions
ps = scc.p; // C(ps,ps) is the permuted matrix
rs = scc.r; // kth block is rs[k]..rs[k+1]-1
nb1 = scc.nb; // # of blocks of A(R2,C2)
for (k = 0; k < nc; k++)
{
s[k] = q[ps[k] + cc[2]];
}
for (k = 0; k < nc; k++)
{
q[k + cc[2]] = s[k];
}
for (k = 0; k < nc; k++)
{
r[k] = p[ps[k] + rr[1]];
}
for (k = 0; k < nc; k++)
{
p[k + rr[1]] = r[k];
}
nb2 = 0; // create the fine block partitions
r[0] = s[0] = 0;
if (cc[2] > 0)
{
nb2++; // leading coarse block A (R1, [C0 C1])
}
for (k = 0; k < nb1; k++) // coarse block A (R2,C2)
{
r[nb2] = rs[k] + rr[1]; // A (R2,C2) splits into nb1 fine blocks
s[nb2] = rs[k] + cc[2];
nb2++;
}
if (rr[2] < m)
{
r[nb2] = rr[2]; // trailing coarse block A ([R3 R0], C3)
s[nb2] = cc[3];
nb2++;
}
r[nb2] = m;
s[nb2] = n;
result.nb = nb2;
// Remove unused space
Array.Resize(ref result.r, nb2 + 1);
Array.Resize(ref result.s, nb2 + 1);
return(result);
}
/// <summary>
/// Generate minimum degree ordering of A+A' (if A is symmetric) or A'A.
/// </summary>
/// <param name="A">Column-compressed matrix</param>
/// <param name="order">Column ordering method</param>
/// <returns>amd(A+A') if A is symmetric, or amd(A'A) otherwise, null on
/// error or for natural ordering</returns>
/// <remarks>
/// See Chapter 7.1 (Fill-reducing orderings: Minimum degree ordering) in
/// "Direct Methods for Sparse Linear Systems" by Tim Davis.
/// </remarks>
public static int[] Generate <T>(CompressedColumnStorage <T> A, ColumnOrdering order)
where T : struct, IEquatable <T>, IFormattable
{
int[] Cp, Ci, P, W, nv, next, head, elen, degree, w, hhead;
int d, dk, dext, lemax = 0, e, elenk, eln, i, j, k, k1,
k2, k3, jlast, ln, dense, nzmax, mindeg = 0, nvi, nvj, nvk, mark, wnvi,
cnz, nel = 0, p, p1, p2, p3, p4, pj, pk, pk1, pk2, pn, q, n;
bool ok;
int h;
n = A.ColumnCount;
if (order == ColumnOrdering.Natural)
{
// TODO: return null here?
return(Permutation.Create(n));
}
var C = ConstructMatrix(SymbolicColumnStorage.Create(A), order);
Cp = C.ColumnPointers;
cnz = Cp[n];
// Find dense threshold
dense = Math.Max(16, 10 * (int)Math.Sqrt(n));
dense = Math.Min(n - 2, dense);
// add elbow room to C
if (!C.Resize(cnz + cnz / 5 + 2 * n))
{
return(null);
}
P = new int[n + 1]; // allocate result
W = new int[n + 1]; // get workspace
w = new int[n + 1];
degree = new int[n + 1];
elen = new int[n + 1]; // Initialized to 0's
// Initialize quotient graph
for (k = 0; k < n; k++)
{
W[k] = Cp[k + 1] - Cp[k];
}
W[n] = 0;
nzmax = C.RowIndices.Length;
Ci = C.RowIndices;
for (i = 0; i <= n; i++)
{
P[i] = -1;
w[i] = 1; // node i is alive
degree[i] = W[i]; // degree of node i
}
next = new int[n + 1];
hhead = new int[n + 1];
head = new int[n + 1];
nv = new int[n + 1];
Array.Copy(P, next, n + 1);
Array.Copy(P, head, n + 1); // degree list i is empty
Array.Copy(P, hhead, n + 1); // hash list i is empty
Array.Copy(w, nv, n + 1); // node i is just one node
mark = Clear(0, 0, w, n); // clear w
elen[n] = -2; // n is a dead element
Cp[n] = -1; // n is a root of assembly tree
w[n] = 0; // n is a dead element
// Initialize degree lists
for (i = 0; i < n; i++)
{
d = degree[i];
if (d == 0) // node i is empty
{
elen[i] = -2; // element i is dead
nel++;
Cp[i] = -1; // i is a root of assembly tree
w[i] = 0;
}
else if (d > dense) // node i is dense
{
nv[i] = 0; // absorb i into element n
elen[i] = -1; // node i is dead
nel++;
Cp[i] = -(n + 2); // FLIP(n)
nv[n]++;
}
else
{
if (head[d] != -1)
{
P[head[d]] = i;
}
next[i] = head[d]; // put node i in degree list d
head[d] = i;
}
}
while (nel < n) // while (selecting pivots) do
{
// Select node of minimum approximate degree
for (k = -1; mindeg < n && (k = head[mindeg]) == -1; mindeg++)
{
;
}
if (next[k] != -1)
{
P[next[k]] = -1;
}
head[mindeg] = next[k]; // remove k from degree list
elenk = elen[k]; // elenk = |Ek|
nvk = nv[k]; // # of nodes k represents
nel += nvk; // nv[k] nodes of A eliminated
// Garbage collection
if (elenk > 0 && cnz + mindeg >= nzmax)
{
for (j = 0; j < n; j++)
{
if ((p = Cp[j]) >= 0) // j is a live node or element
{
Cp[j] = Ci[p]; // save first entry of object
Ci[p] = -(j + 2); // first entry is now CS_FLIP(j)
}
}
for (q = 0, p = 0; p < cnz;) // scan all of memory
{
if ((j = FLIP(Ci[p++])) >= 0) // found object j
{
Ci[q] = Cp[j]; // restore first entry of object
Cp[j] = q++; // new pointer to object j
for (k3 = 0; k3 < W[j] - 1; k3++)
{
Ci[q++] = Ci[p++];
}
}
}
cnz = q; // Ci [cnz...nzmax-1] now free
}
// Construct new element
dk = 0;
nv[k] = -nvk; // flag k as in Lk
p = Cp[k];
pk1 = (elenk == 0) ? p : cnz; // do in place if elen[k] == 0
pk2 = pk1;
for (k1 = 1; k1 <= elenk + 1; k1++)
{
if (k1 > elenk)
{
e = k; // search the nodes in k
pj = p; // list of nodes starts at Ci[pj]*/
ln = W[k] - elenk; // length of list of nodes in k
}
else
{
e = Ci[p++]; // search the nodes in e
pj = Cp[e];
ln = W[e]; // length of list of nodes in e
}
for (k2 = 1; k2 <= ln; k2++)
{
i = Ci[pj++];
if ((nvi = nv[i]) <= 0)
{
continue; // node i dead, or seen
}
dk += nvi; // degree[Lk] += size of node i
nv[i] = -nvi; // negate nv[i] to denote i in Lk
Ci[pk2++] = i; // place i in Lk
if (next[i] != -1)
{
P[next[i]] = P[i];
}
if (P[i] != -1) // remove i from degree list
{
next[P[i]] = next[i];
}
else
{
head[degree[i]] = next[i];
}
}
if (e != k)
{
Cp[e] = -(k + 2); // absorb e into k // FLIP(k)
w[e] = 0; // e is now a dead element
}
}
if (elenk != 0)
{
cnz = pk2; // Ci [cnz...nzmax] is free
}
degree[k] = dk; // external degree of k - |Lk\i|
Cp[k] = pk1; // element k is in Ci[pk1..pk2-1]
W[k] = pk2 - pk1;
elen[k] = -2; // k is now an element
// Find set differences
mark = Clear(mark, lemax, w, n); // clear w if necessary
for (pk = pk1; pk < pk2; pk++) // scan 1: find |Le\Lk|
{
i = Ci[pk];
if ((eln = elen[i]) <= 0)
{
continue; // skip if elen[i] empty
}
nvi = -nv[i]; // nv [i] was negated
wnvi = mark - nvi;
for (p = Cp[i]; p <= Cp[i] + eln - 1; p++) // scan Ei
{
e = Ci[p];
if (w[e] >= mark)
{
w[e] -= nvi; // decrement |Le\Lk|
}
else if (w[e] != 0) // ensure e is a live element
{
w[e] = degree[e] + wnvi; // 1st time e seen in scan 1
}
}
}
// Degree update
for (pk = pk1; pk < pk2; pk++) // scan2: degree update
{
i = Ci[pk]; // consider node i in Lk
p1 = Cp[i];
p2 = p1 + elen[i] - 1;
pn = p1;
for (h = 0, d = 0, p = p1; p <= p2; p++) // scan Ei
{
e = Ci[p];
if (w[e] != 0) // e is an unabsorbed element
{
dext = w[e] - mark; // dext = |Le\Lk|
if (dext > 0)
{
d += dext; // sum up the set differences
Ci[pn++] = e; // keep e in Ei
h += e; // compute the hash of node i
}
else
{
Cp[e] = -(k + 2); // aggressive absorb. e.k // FLIP(k)
w[e] = 0; // e is a dead element
}
}
}
elen[i] = pn - p1 + 1; // elen[i] = |Ei|
p3 = pn;
p4 = p1 + W[i];
for (p = p2 + 1; p < p4; p++) // prune edges in Ai
{
j = Ci[p];
if ((nvj = nv[j]) <= 0)
{
continue; // node j dead or in Lk
}
d += nvj; // degree(i) += |j|
Ci[pn++] = j; // place j in node list of i
h += j; // compute hash for node i
}
if (d == 0) // check for mass elimination
{
Cp[i] = -(k + 2); // absorb i into k // FLIP(k)
nvi = -nv[i];
dk -= nvi; // |Lk| -= |i|
nvk += nvi; // |k| += nv[i]
nel += nvi;
nv[i] = 0;
elen[i] = -1; // node i is dead
}
else
{
degree[i] = Math.Min(degree[i], d); // update degree(i)
Ci[pn] = Ci[p3]; // move first node to end
Ci[p3] = Ci[p1]; // move 1st el. to end of Ei
Ci[p1] = k; // add k as 1st element in of Ei
W[i] = pn - p1 + 1; // new len of adj. list of node i
h = ((h < 0) ? (-h) : h) % n; // finalize hash of i
next[i] = hhead[h]; // place i in hash bucket
hhead[h] = i;
P[i] = h; // save hash of i in last[i]
}
} // scan2 is done
degree[k] = dk; // finalize |Lk|
lemax = Math.Max(lemax, dk);
mark = Clear(mark + lemax, lemax, w, n); // clear w
// Supernode detection
for (pk = pk1; pk < pk2; pk++)
{
i = Ci[pk];
if (nv[i] >= 0)
{
continue; // skip if i is dead
}
h = P[i]; // scan hash bucket of node i
i = hhead[h];
hhead[h] = -1; // hash bucket will be empty
for (; i != -1 && next[i] != -1; i = next[i], mark++)
{
ln = W[i];
eln = elen[i];
for (p = Cp[i] + 1; p <= Cp[i] + ln - 1; p++)
{
w[Ci[p]] = mark;
}
jlast = i;
for (j = next[i]; j != -1;) // compare i with all j
{
ok = (W[j] == ln) && (elen[j] == eln);
for (p = Cp[j] + 1; ok && p <= Cp[j] + ln - 1; p++)
{
if (w[Ci[p]] != mark)
{
ok = false; // compare i and j
}
}
if (ok) // i and j are identical
{
Cp[j] = -(i + 2); // absorb j into i // FLIP(i)
nv[i] += nv[j];
nv[j] = 0;
elen[j] = -1; // node j is dead
j = next[j]; // delete j from hash bucket
next[jlast] = j;
}
else
{
jlast = j; // j and i are different
j = next[j];
}
}
}
}
// Finalize new element
for (p = pk1, pk = pk1; pk < pk2; pk++) // finalize Lk
{
i = Ci[pk];
if ((nvi = -nv[i]) <= 0)
{
continue; // skip if i is dead
}
nv[i] = nvi; // restore nv[i]
d = degree[i] + dk - nvi; // compute external degree(i)
d = Math.Min(d, n - nel - nvi);
if (head[d] != -1)
{
P[head[d]] = i;
}
next[i] = head[d]; // put i back in degree list
P[i] = -1;
head[d] = i;
mindeg = Math.Min(mindeg, d); // find new minimum degree
degree[i] = d;
Ci[p++] = i; // place i in Lk
}
nv[k] = nvk; // # nodes absorbed into k
if ((W[k] = p - pk1) == 0) // length of adj list of element k
{
Cp[k] = -1; // k is a root of the tree
w[k] = 0; // k is now a dead element
}
if (elenk != 0)
{
cnz = p; // free unused space in Lk
}
}
// Postordering
for (i = 0; i < n; i++)
{
Cp[i] = -(Cp[i] + 2); // fix assembly tree // FLIP(Cp[i])
}
for (j = 0; j <= n; j++)
{
head[j] = -1;
}
for (j = n; j >= 0; j--) // place unordered nodes in lists
{
if (nv[j] > 0)
{
continue; // skip if j is an element
}
next[j] = head[Cp[j]]; // place j in list of its parent
head[Cp[j]] = j;
}
for (e = n; e >= 0; e--) // place elements in lists
{
if (nv[e] <= 0)
{
continue; // skip unless e is an element
}
if (Cp[e] != -1)
{
next[e] = head[Cp[e]]; // place e in list of its parent
head[Cp[e]] = e;
}
}
for (k = 0, i = 0; i <= n; i++) // postorder the assembly tree
{
if (Cp[i] == -1)
{
k = GraphHelper.TreeDepthFirstSearch(i, k, head, next, P, w);
}
}
return(P);
}
/// <summary>
/// Compute strongly connected components of matrix.
/// </summary>
/// <param name="matrix">column-compressed matrix</param>
/// <returns>Strongly connected components</returns>
public static StronglyConnectedComponents Generate <T>(CompressedColumnStorage <T> matrix)
where T : struct, IEquatable <T>, IFormattable
{
return(Generate(SymbolicColumnStorage.Create(matrix), matrix.ColumnCount));
}
