p?dttrf
Computes the LU factorization of a diagonally dominantlike tridiagonal distributed matrix.
Syntax

call psdttrf(n, dl, d, du, ja, desca, af, laf, work, lwork, info)
call pddttrf(n, dl, d, du, ja, desca, af, laf, work, lwork, info)
call pcdttrf(n, dl, d, du, ja, desca, af, laf, work, lwork, info)
call pzdttrf(n, dl, d, du, ja, desca, af, laf, work, lwork, info)
Include Files
Description
The p?dttrfroutine computes the LU factorization of an nbyn real/complex diagonally dominantlike tridiagonal distributed matrix A(1:n, ja:ja+n1) without pivoting for stability.
The resulting factorization is not the same factorization as returned from LAPACK. Additional permutations are performed on the matrix for the sake of parallelism.
The factorization has the form:
A(1:n, ja:ja+n1) = P*L*U*P^{T},
where P is a permutation matrix, and L and U are banded lower and upper triangular matrices, respectively.
Optimization Notice 

Intel's compilers may or may not optimize to the same degree for nonIntel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessordependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice. Notice revision #20110804 
Input Parameters
 n

(global) INTEGER. The number of rows and columns to be operated on, that is, the order of the distributed submatrix A(1:n, ja:ja+n1) (n≥ 0).
 dl, d, du

(local)
REAL for pspttrf
DOUBLE PRECISON for pdpttrf
COMPLEX for pcpttrf
DOUBLE COMPLEX for pzpttrf.
Pointers to the local arrays of size nb_a each.
On entry, the array dl contains the local part of the global vector storing the subdiagonal elements of the matrix. Globally, dl(1) is not referenced, and dl must be aligned with d.
On entry, the array d contains the local part of the global vector storing the diagonal elements of the matrix.
On entry, the array du contains the local part of the global vector storing the superdiagonal elements of the matrix. du(n) is not referenced, and du must be aligned with d.
 ja

(global) INTEGER. The index in the global matrix A indicating the start of the matrix to be operated on (which may be either all of A or a submatrix of A).
 desca

(global and local) INTEGER array of size dlen_. The array descriptor for the distributed matrix A.
If dtype_a = 501, then dlen_≥ 7;
else if dtype_a = 1, then dlen_≥ 9.
 laf

(local) INTEGER. The size of the array af.
Must be laf≥ 2*(NB+2) .
If laf is not large enough, an error code will be returned and the minimum acceptable size will be returned in af(1).
 work

(local) Same type as d. Workspace array of size lwork.
 lwork

(local or global) INTEGER. The size of the work array, must be at least lwork≥ 8*NPCOL.
Output Parameters
 dl, d, du

On exit, overwritten by the information containing the factors of the matrix.
 af

(local)
REAL for psdttrf
DOUBLE PRECISION for pddttrf
COMPLEX for pcdttrf
DOUBLE COMPLEX for pzdttrf.
Array of size laf.
Auxiliary fillin space. The fillin space is created in a call to the factorization routine p?dttrf and is stored in af.
Note that if a linear system is to be solved using p?dttrs after the factorization routine,af must not be altered.
 work(1)

On exit, work(1) contains the minimum value of lwork required for optimum performance.
 info

(global) INTEGER.
If info=0, the execution is successful.
info < 0:
If the ith argument is an array and the jth entry had an illegal value, then info = (i*100+j); if the ith argument is a scalar and had an illegal value, then info = i.
info> 0:
If info = k ≤ NPROCS, the submatrix stored on processor info and factored locally was not diagonally dominantlike, and the factorization was not completed.
If info = k > NPROCS, the submatrix stored on processor infoNPROCS representing interactions with other processors was not nonsingular, and the factorization was not completed.