vslSkipAheadStreamEx

Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

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ID 766686

Date 7/13/2023

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vslSkipAheadStreamEx

Initializes a stream using the block-splitting method with partitioned number of skipped elements.

Syntax

status = vslskipAheadstreamEx( stream, n, nskip )

Include Files

mkl.fi, mkl_vsl.f90

Input Parameters

Name	Type	Description
stream	TYPE(VSL_STREAM_STATE), INTENT(IN)	Pointer to the stream state structure to which block-splitting method is applied
n	INTEGER, INTENT(IN)	Number of summands in nskip
nskip	INTEGER(KIND=8), INTENT(IN)	Partitioned number of skipped elements

Description

The vslSkipAheadStreamEx function skips a given number of elements in a random stream. This feature is particularly useful in distributing random numbers from original random stream across different computational nodes. If the largest number of random numbers used by a computational node is nskip, then the original random sequence may be split by vslSkipAheadStreamEx into non-overlapping blocks of nskip size so that each block corresponds to the respective computational node. The number of computational nodes is unlimited. This method is known as the block-splitting method or as the skip-ahead method.

Use this function when the number of elements to skip in a random stream is greater than 2⁶³. Prior calls to the function represent the number of skipped elements with array of size n as shown below:

nskip[0]+ nskip[1]*2⁶⁴+nskip[2]* 2¹²⁸+ … +nskip[n-1]*2^{(64*(n-1) )};

When the number of skipped elements is less than 2⁶³ you can use either vslSkipAheadtreamEx or vslSkipAheadStream. The following code illustrates how to initialize three independent streams using the vslSkipAheadStreamEx function:

...
type(VSL_STREAM_STATE) ::stream1 type(VSL_STREAM_STATE) ::stream2 type(VSL_STREAM_STATE) ::stream3

! Creating the 1st stream
status = vslnewstream(stream1, VSL_BRNG_MRG32K3A, 174)

! To skip 2^64 elements in the random stream skipaheadstreamEx(nskip) function should !	be called with nskip represented as nskip = 2^64 = 0 + 1 * 2^64
integer(kind=8) nskip(2) 
nskip(1) = 0
nskip(2) = 1

! Skipping ahead by 2^64 elements the 2nd stream
status = vslcopystream(stream2, stream1)
status = vslskipaheadstreamex (stream2, 2, nskip)

! Skipping ahead by 2^64 elements the 3rd stream
status = vslcopystream(stream3, stream2)
status = vslskipaheadstreamex (stream3, 2, nskip)

! Generating random numbers
...

! Deleting the streams
status = vsldeletestream(stream1)
status = vsldeletestream(stream2)
status = vsldeletestream(stream3)
...

Return Values

VSL_ERROR_OK, VSL_STATUS_OK: Indicates no error, execution is successful.
VSL_ERROR_NULL_PTR: stream is a NULL pointer.
VSL_RNG_ERROR_BAD_STREAM: stream is not a valid random stream.
VSL_RNG_ERROR_SKIPAHEADEX_UNSUPPORTED: BRNG does not support the advanced Skip-Ahead method.

Parent topic: Service Routines

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Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

vslSkipAheadStreamEx

Syntax

Include Files

Input Parameters

Description

Return Values