>> ldldemo

 
  LDL:  factorization of a real sparse symmetric matrix.
 
 	[L, D, Parent, fl] = ldl (A)
 	[L, D, Parent, fl] = ldl (A, P)
 	[x, fl] = ldl (A, [ ], b)
 	[x, fl] = ldl (A, P, b)
 
  Let I = speye (size (A,1)). The factorization is (L+I)*D*(L+I)' = A or A(P,P).
  A must be sparse, square, and real.  Only the diagonal and upper triangular
  part of A or A(P,P) are accessed.  L is lower triangular with unit diagonal,
  but the diagonal is not returned.  D is a diagonal sparse matrix.  P is either
  a permutation of 1:n, or an empty vector, where n = size (A,1).  If not
  present, or empty, then P=1:n is assumed.  Parent is the elimination tree of
  A or A(P,P).  If positive, fl is the floating point operation count, or
  negative if any entry on the diagonal of D is zero.
 
  In the x = ldl (A, P, b) usage, the LDL' factorization is not returned.
  Instead, the system A*x=b is solved for x, where both b and x are dense.
 
  If a zero entry on the diagonal of D is encountered, the LDL' factorization is
  terminated at that point.  If there is no fl output argument, an error occurs.
  Otherwise, fl is negative, and let d=-fl.  D(d,d) is the first zero entry on
  the diagonal of D.  A partial factorization is returned.  Let B = A, or A(P,P)
  if P is present.  Let F = (L+I)*D*(L+I)'.  Then F (1:d,1:d) = B (1:d,1:d).
  Rows d+1 to n of L and D are all zero.
 
  See also CHOL, LDLSYMBOL, SYMBFACT, ETREE
 
  LDL Version 1.0 (Dec. 31, 2003), Copyright (c) 2003 by Timothy A Davis,
  University of Florida.  All Rights Reserved.  See README for the License.

Compiling ldl and ldlsymbol:

Testing ldl and ldlsymbol:
norm (LDL'-PAP') = 6.51562e-15
residual 3.55986e-15 for ldl, flops    14813.0
residual 3.86691e-15 for ldl solve
residual 3.79296e-15 for ldlrow.m
norm (LDL'-PAP') = 6.63575e-15
residual 2.96267e-15 for ldl, flops    14813.0
residual 3.53833e-15 for ldl solve

Original matrix: nz in L:  2206  flop count: 81044
Permuted matrix: nz in L:   893  flop count: 14813

ldldemo: all tests passed
>> diary off