lapack
Table of Content
Versions and Availability
About the Software
LAPACK is written in Fortran90 and provides routines for solving systems of simultaneous linear equations, least-squares solutions of linear systems of equations, eigenvalue problems, and singular value problems. - Homepage: http://www.netlib.org/lapack/
Usage
LAPACK is a binary library, so it is linked to your program by the
compiler during the build process by adding the -llapack
flag to the link line:
Fortran
$ ifort sample.f -llapack
Open Fortran Example?
Fortran Source
!********************************************** ! THIS EXAMPLE USES THE LAPACK ROUTINE DGESV ! TO SOLVE A SYSTEM OF LINEAR EQUATIONS AX=B ! A = [1, 2, 3; 4, 5, 6; 7, 8 10] ! B = [1, 0; 0, 1; 0, 0] ! ********************************************* program lapack_test integer ipiv(3), info, i, j double precision A(3,3), B(3,2) A(1,1)=1 A(1,2)=2 A(1,3)=3 A(2,1)=4 A(2,2)=5 A(2,3)=6 A(3,1)=7 A(3,2)=8 A(3,3)=10 B(1,1)=1 B(2,1)=0 B(3,1)=0 B(1,2)=0 B(2,2)=1 B(3,2)=0 call dgesv (3,2,A,3,ipiv,B,3,info) if(info .EQ. 0) then do i=1,3 write(*,'(2F8.3)') (B(i,j), j=1,2) enddo endif end program lapack_test
Build and Execute
$ ifort lapack_test.f90 -llapack $ ./a.out -0.667 -1.333 -0.667 3.667 1.000 -2.000
C
The LAPACK routines must be declared with extern
,
the routine name must be in lowercase, and it must be followed by
an _ (i.e. underscore):
extern void dgetrf_(int*, int*, double*, int*, int*, int*);
Be sure when calling the LAPACK routing that all arguments are passed by reference.
Note: Since C matrices are stored in row major order, and Fortran matrices are stored in column major order, a transpose is necessary to go from C to Fortran order, and the result transposed again from Fortran to C order. It is more efficient to change the array indexing to take this into account.
$ icc sample.c -llapack
Open C Example?
C Source
$ cat lapack_test.c /********************************************** * THIS EXAMPLE USES THE LAPACK ROUTINE DGESV * TO SOLVE A SYSTEM OF LINEAR EQUATIONS AX=B * A = [1, 2, 3; 4, 5, 6; 7, 8 10] * B = [1, 0; 0, 1; 0, 0] **********************************************/ #includeextern void dgesv_(int*, int*, double*, int*, int*, double*, int*, int*); int main() { int n, nrhs, lda, ldb, IPIV[3], info, i; double A[3][3], B[2][3]; // Matrices must be transposed A[0][0] = 1; A[1][0] = 2; A[2][0] = 3; A[0][1] = 4; A[1][1] = 5; A[2][1] = 6; A[0][2] = 7; A[1][2] = 8; A[2][2] = 10; B[0][0] = 1; B[0][1] = 0; B[0][2] = 0; B[1][0] = 0; B[1][1] = 1; B[1][2] = 0; n = 3; nrhs = 2; lda = 3; ldb = 3; dgesv_(&n, &nrhs, (double *)A, &lda, IPIV, (double *)B, &ldb, &info); if(info == 0) { for(i = 0; i < 3; i++) printf("%8.3f %8.3f\n", B[0][i], B[1][i]); } }
Build and Execute
C++
The LAPACK routines must be declared with extern
"C"
, the routine name must be in lowercase, and it must
be followed by an _ (i.e. underscore):
extern "C" void dgetrf_(int*, int*, double*, int*, int*, int*);
Be sure when calling the LAPACK routing that all arguments are passed by reference.
Note: Since C++ matrices are stored in row major order, and Fortran matrices are stored in column major order, a transpose is necessary to go from C to Fortran order, and the result transposed again from Fortran to C order. It is more efficient to change the array indexing to take this into account.
$ icpc sample.c -llapack
Open C++ Example?
C Source
$ cat lapack_test.c /********************************************** * THIS EXAMPLE USES THE LAPACK ROUTINE DGESV * TO SOLVE A SYSTEM OF LINEAR EQUATIONS AX=B * A = [1, 2, 3; 4, 5, 6; 7, 8 10] * B = [1, 0; 0, 1; 0, 0] **********************************************/ #includeextern void dgesv_(int*, int*, double*, int*, int*, double*, int*, int*); int main() { int n, nrhs, lda, ldb, IPIV[3], info, i; double A[3][3], B[2][3]; // Matrices must be transposed A[0][0] = 1; A[1][0] = 2; A[2][0] = 3; A[0][1] = 4; A[1][1] = 5; A[2][1] = 6; A[0][2] = 7; A[1][2] = 8; A[2][2] = 10; B[0][0] = 1; B[0][1] = 0; B[0][2] = 0; B[1][0] = 0; B[1][1] = 1; B[1][2] = 0; n = 3; nrhs = 2; lda = 3; ldb = 3; dgesv_(&n, &nrhs, (double *)A, &lda, IPIV, (double *)B, &ldb, &info); if(info == 0) { for(i = 0; i < 3; i++) printf("%8.3f %8.3f\n", B[0][i], B[1][i]); } }
Build and Execute
Resources
- LAPACK Users Guide
- Individual LAPACK routines are documented in their own man page.
To get more information on a given routine, use the command:
$ man routine_name
For example, to get informantion on
dgesvd
:$ man dgesvd
Last modified: September 10 2020 11:58:50.