/// <summary>
/// Symbolic ordering and analysis for QR
/// </summary>
static SymbolicFactorization SymbolicAnalysis(int order, SparseMatrix A)
{ // ori: cs_sqr
int n = A.n, k;
bool ok = true;
int[] post;
SymbolicFactorization S = new SymbolicFactorization(); // allocate result S
S.q = Ordering.AMD(order, A); // fill-reducing ordering
if (order != 0 && S.q == null)
{
return(null);
}
SparseMatrix C = order > 0 ? (SparseMatrix)A.Permute(null, S.q, false) : A;
S.parent = Common.EliminationTree(C, true); // etree of C'*C, where C=A(:,q)
post = Common.TreePostorder(S.parent, n);
S.cp = Common.ColumnCounts(C, S.parent, post, true); // col counts chol(C'*C)
ok = C != null && S.parent != null && S.cp != null && CountV(C, S);
if (ok)
{
for (S.unz = 0, k = 0; k < n; k++)
{
S.unz += S.cp[k];
}
}
ok = ok && S.lnz >= 0 && S.unz >= 0; // int overflow guard
return(ok ? S : null); // return result S
}
