S3L_acorr

Description

S3L_acorr computes the 1D or 2D autocorrelation of a signal represented by the parallel array described by S3L array handle a. The result is stored in the parallel array described by the S3L array handle c.

a and c are of the same real or complex type.

For the 1D case, if a is of length ma, the result of the autocorrelation will be of length 2*ma-1. In the 2D case, if a is of size [ma,na], the result of the autocorrelation is of size [2*ma-1,2*na-1].

The size of c has to be at least equal to the size of the autocorrelation for each case, as described above. If it is larger, the excess elements of c will contain zero or non-significant entries.

The result of the autocorrelation of a is stored in wrap-around order along each dimension. If the extent of c along a given axis is lc, the autocorrelation at zero lag is stored in c(0), the autocorrelation at lag 1 in c(1), and so forth. The autocorrelation at lag -1 is stored in c(lc-1), the autocorrelation at lag -2 is stored in c(lc-2), and so forth.

Side Effects

Following calculation of the autocorrelation of a, a may be destroyed, since it is used internally as auxiliary storage. If its contents will be reused after autocorrelation is performed, first copy it to a temporary array.

S3L_acorr is most efficient when all arrays have the same length and when this length is one that can be computed efficiently via S3L_fft, or S3L_rc_fft. See "S3L_fft " and "S3L_rc_fft and S3L_cr_fft " for more information about execution efficiency.

Restriction

The dimensions of array c must be such that a 1D or 2D complex-to-complex FFT or real-to-complex FFT can be computed.

Syntax

The C and Fortran syntax for S3L_acorr are shown below.

C/C++ Syntax

Example 8-88

#include <s3l/s3l-c.h>
#include <s3l/s3l_errno-c.h>
int
S3L_acorr(a, c, setup_id)
    S3L_array_t       a
    S3L_array_t       c
    int               setup_id

F77/F90 Syntax

Example 8-89

include `s3l/s3l-f.h'
include `s3l/s3l_errno-f.h'
subroutine
S3L_acorr(a, c, setup_id, ier)
    integer*8         a
    integer*8         c
    integer*4         setup_id
    integer*4         ier

where <type> is real*4 or real*8 for both C/C++ and F77/F90.

Input

• a - S3L internal array handle for the parallel array upon which the autocorrelation will be performed. a is of size ma (1D case) or ma x na (2D case).

• setup_id - Integer value returned by a previous call to S3L_acorr_setup.

Output

This function uses the following arguments for output:

• c - S3L internal array handle for the parallel array that contains the results of the autocorrelation. Its length must be at least 2*ma-1 (1D case) or 2*ma-1 x 2*na-1 (2D case).

• ier (Fortran only) - When called from a Fortran program, this function returns error status in ier.

Error Handling

On success, S3L_acorr_setup returns S3L_SUCCESS.

S3L_acorr_setup performs generic checking of the arrays it accepts as arguments. If an array argument contains an invalid or corrupted value, the function terminates and an error code indicating which value of the array handle was invalid is returned. See Appendix A of this manual for a detailed list of these error codes.

In addition, the following conditions cause the function to terminate and return one of the following codes:

• S3L_ERR_ARG_DTYPE - The data type of one of the array arguments is invalid. It must be one of:

  • S3L_float

  • S3L_double

  • S3L_complex

  • S3L_double_complex

• S3L_ERR_MATCH_DTYPE - The array arguments are not of the same data type.

• S3L_ERR_MATCH_RANK - The array arguments are not of the same rank.

• S3L_ERR_ARG_RANK - The rank of one of the array arguments is not 1 or 2 as required.

• S3L_ERR_ARG_EXTENTS - The extents of c are smaller than 2*ma-1 (1D case) or 2*ma-1 x 2*na-1 (2D case).

In addition, since S3L_fft or S3L_rc_fft is used internally to compute the autocorrelation, if the dimensions of c are not suitable for S3L_fft or S3L_rc_fft, an error code indicating this unsuitability is returned. For more details, refer to the man pages for S3L_fft and S3L_rc_fft.

Examples

../examples/s3l/acorr/ex_acorr.c
../examples/s3l/acorr-f/ex_acorr.f

Related Functions

S3L_acorr_setup(3)
S3L_acorr_free_setup(3)