PCBDDC: solved warning from gcc for uninitialized variables

PCBDDC: Use MatISGetMPIXAIJ for global change of variables

PCBDDC; optimized PCBDDCSetUpCorrection

now used MatMatSolve whenever possible
extensive usage of BLAS whenever possible

PCBDDC: added initial implementation for adaptive selection of constraints

positive definite case covered only
untested for complex

generalized eigenvalue problem is inv(sum(inv(S_F))) = lambda inv

PCBDDC: added initial implementation for adaptive selection of constraints

positive definite case covered only
untested for complex

generalized eigenvalue problem is inv(sum(inv(S_F))) = lambda inv(sum(inv(St_F)))
this is the right one for 2D problems and for faces in 3D; it is an heuristic for edges in 3D

tested with H(div) and H(curl) (3D) and works like a charm

cholesky support for matrix inversion should still be added

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PCBDDC; added slot for threshold when adaptively computing constraints

PCBDDC; clean up of sub_schurs/deluxe code

* options database are now part of sub_schurs setup
* eliminated unneeded field from sub_schurs structure
* added 2 interface functions to init and setup s

PCBDDC; clean up of sub_schurs/deluxe code

* options database are now part of sub_schurs setup
* eliminated unneeded field from sub_schurs structure
* added 2 interface functions to init and setup sub_schurs when setupping the preconditioner
* if a change of basis is requested, releveant matrices are projected
* still need to be tested when the BDDC is reused

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PCBDDC: add function to extract sequential matrices from parallel or sequential matrices using unordered index sets

This is just to allow code reuse inside PCBDDC

PCBDDC: added a second sub_schurs structure to pcbddc data structure

Begin reorganization of SubSchurs code for code reuse for adaptive selection of constraints

PCBDDC; split computation of local solvers

PCIS: added reusability of PCISSetUp

PCBDDC: make sub_schurs a member of PC_BDDC data structure

Merge branch 'stefano_zampini/pcbddcgraph-improve'

PCBDDC: added support for detecting disconnected subdomains if no CSR info is used

this can be useful in face- or edge-based discretizaions like RT ot Nedelec elements

Merge branch 'barry/remove-unneeded-paren-petscmalloc'

Conflicts:
src/mat/impls/baij/seq/baij.c

Merge branch 'master' into mlange/refactor-plex-distribute

Conflicts:
src/dm/impls/plex/examples/tests/output/ex12_1.out
src/dm/impls/plex/examples/tests/output/ex12_2.out

PCBDDC: no need to reorder the constraints in local ordering after SVD

This also guaranties that the change of basis computed with QR will be coherent among processes
It also extends the reordering

PCBDDC: no need to reorder the constraints in local ordering after SVD

This also guaranties that the change of basis computed with QR will be coherent among processes
It also extends the reordering to the case of using QR on a single cc

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PCBDDC: fixed bug when using more than 1 constraint per connected component via SVD

The bug originated from the (wrong!) assumption that the returned eigenmodes from the SVD would be consistent amon

PCBDDC: fixed bug when using more than 1 constraint per connected component via SVD

The bug originated from the (wrong!) assumption that the returned eigenmodes from the SVD would be consistent among sharing processes
This is not true since the computed SVD depends on the local ordering of dofs and each process computes its own SVD (separately for each connected component).
The fix consists in ordering the constrained indices consistently across processes by using global ordering

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Merge branch 'stefano_zampini/fixes-for-raviart-thomas'

Merge branch 'stefano_zampini/fixes-and-improvements-multilevel'

PCBDDC: avoid LAPACK calls if either nnsp_true or just one constraint per cc is required

PCBDDC: fix wrong computation of change of basis blocks

The last column of the block should be given by the orthonormalized coefficients of the quadrature rule
Note that the computed block is the sa

PCBDDC: fix wrong computation of change of basis blocks

The last column of the block should be given by the orthonormalized coefficients of the quadrature rule
Note that the computed block is the same as before if computed with respect the arithmetic average

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PCBDDC: QR decomposition for change of basis can now be also used for connected components with only 1 constraint

This partially solves the following issue with Raviart Thomas elements
Using standar

PCBDDC: QR decomposition for change of basis can now be also used for connected components with only 1 constraint

This partially solves the following issue with Raviart Thomas elements
Using standard change of basis, the coarse matrix produced is singular and CG doesn't converge to the exact solution (even if the eigenvalues of the preconditioned operator are the same of the unchanged basis case)
On the other hand, using QR, CG converges to the exact solution but the eigenvalues of the preconditioned operator are very different from not using the change of basis.
Still needs to be investigated...

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convert some PetscMalloc() to PetscMalloc1()
remove unneeded () in first argument to PetscMalloc/Calloc1()
fixes for MATLAB examples

PCBDDC; forgot to remove debugging print

Merge branch 'stefano_zampini/fixes-and-improvements-multilevel'