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NBLK

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NBLK = [integer] 

Default: NBLK = -1 VASP.4.6
= 256 in VASP.5.2, if dfast

Description: NBLK determines the blocking factor in many BLAS level 3 routines.


In some cases, VASP has to perform a unitary transformation of the current orbitals. This is done using a work array CBLOCK and the following FORTRAN code:

      DO 100 IBLOCK=0,NPL-1,NBLK
         ILEN=MIN(NBLK,NPL-IBLOCK)
         DO 200 N1=1,N
            DO 200 M=1,ILEN
            CBLOCK(M,N1)=C(M+IBLOCK,N1)
            C(M+IBLOCK,N1)=0
  200    CONTINUE
C        C(IBLOCK+I,N)=SUM_(J,K) CH(I,K) CBLOCK(K,N)
         CALL ZGEMM ('N', 'N', ILEN, N, N, (1.,0.), CBLOCK, NBLK, CH, N,
              &   (1.,0.), C(IBLOCK+1,1), NDIM)
  100 CONTINUE

ZGEMM is the matrix matrix multiplication command of the BLAS package. The task performed by this call is indicated by the comment line written above the ZGEMM call. Generally NBLK=16 or 32 is large enough for super-scalar machines. A large value might be necessary on vector machines for optimal performance (NBLK=128).

Examples that use this tag


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