C Interface Conventions for LAPACK Routines

Developer Reference for Intel® oneAPI Math Kernel Library for C

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ID 766684

Date 11/07/2023

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C Interface Conventions for LAPACK Routines

The C interfaces are implemented for most of the Intel® oneAPI Math Kernel Library (oneMKL) LAPACK driver and computational routines.

NaN Checking in LAPACKE

NaN checking can affect the performance of an application. By default, it is ON.

See the Support Functions section for details on the methods and options to turn NaN check off or back on with LAPACKE:.

Function Prototypes

Intel® oneAPI Math Kernel Library (oneMKL) supports four distinct floating-point precisions. Each corresponding prototype looks similar, usually differing only in the data type. C interface LAPACK function names follow the form<?><name>[_64], where <?> is:

LAPACKE_s for float
LAPACKE_d for double
LAPACKE_c for lapack_complex_float
LAPACKE_z for lapack_complex_double

On 64-bit platforms, Intel® oneAPI Math Kernel Library (oneMKL) provides LAPACK C interfaces with the _64 suffix to support large data arrays in the LP64 interface library. For more interface library details, see "Using the ILP64 Interface vs. LP64 Interface" in the developer guide.

A specific example follows. To solve a system of linear equations with a packed Cholesky-factored Hermitian positive-definite matrix with complex precision, use the following:

lapack_int LAPACKE_cpptrs(int matrix_layout, char uplo, lapack_int n, lapack_int nrhs, const lapack_complex_float* ap, lapack_complex_float* b, lapack_int ldb);

For matrices whose dimensions are greater than 2³¹-1, you can use either LAPACKE_cpptrs in the ILP64 interface library or LAPACKE_cpptrs_64 in the LP64 interface library.

Workspace Arrays

In contrast to the Fortran interface, the LAPACK C interface omits workspace parameters because workspace is allocated during runtime and released upon completion of the function operation.

If you prefer to allocate workspace arrays yourself, the LAPACK C interface provides alternate interfaces with work parameters. The name of the alternate interface is the same as the LAPACK C interface with _work appended. For example, the syntax for the singular value decomposition of a real bidiagonal matrix is:

Fortran:: call sbdsdc ( uplo, compq, n, d, e, u, ldu, vt, ldvt, q, iq, work, iwork, info )
C LAPACK interface:: lapack_int LAPACKE_sbdsdc ( int matrix_layout, char uplo, char compq, lapack_int n, float* d, float* e, float* u, lapack_int ldu, float* vt, lapack_int ldvt, float* q, lapack_int* iq );
Alternate C LAPACK interface with work parameters:: lapack_int LAPACKE_sbdsdc_work( int matrix_layout, char uplo, char compq, lapack_int n, float* d, float* e, float* u, lapack_int ldu, float* vt, lapack_int ldvt, float* q, lapack_int* iq, float* work, lapack_int* iwork );

See the install_dir/include/mkl_lapacke.h file for the full list of alternative C LAPACK interfaces.

The Intel® oneAPI Math Kernel Library (oneMKL) Fortran-specific documentation contains details about workspace arrays.

Mapping Fortran Data Types against C Data Types

Fortran Data Types vs. C Data Types
FORTRAN	C
INTEGER	lapack_int
LOGICAL	lapack_logical
REAL	float
DOUBLE PRECISION	double
COMPLEX	lapack_complex_float
COMPLEX*16/DOUBLE COMPLEX	lapack_complex_double
CHARACTER	char

C Type Definitions

You can find type definitions specific to Intel® oneAPI Math Kernel Library (oneMKL) such asMKL_INT, MKL_Complex8, and MKL_Complex16 in install_dir/mkl_types.h.

C types

#ifndef lapack_int
#define lapack_int MKL_INT
#endif

#ifndef lapack_logical
#define lapack_logical lapack_int
#endif

Complex Type Definitions

Complex type for single precision:

#ifndef lapack_complex_float
#define lapack_complex_float   MKL_Complex8
#endif

Complex type for double precision:

#ifndef lapack_complex_double
#define lapack_complex_double   MKL_Complex16
#endif

Matrix Layout Definitions

#define LAPACK_ROW_MAJOR  101
#define LAPACK_COL_MAJOR  102

See Matrix Layout for LAPACK Routines above for an explanation of row-major order and column-major order storage.

Error Code Definitions

#define LAPACK_WORK_MEMORY_ERROR       -1010  /* Failed to allocate memory  
                                            for a working array */
#define LAPACK_TRANSPOSE_MEMORY_ERROR  -1011  /* Failed to allocate memory 
                                            for transposed matrix */

Parent topic: LAPACK Routines

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