Undefined reference to LAPACK and BLAS subroutines - fortran

Question

I'm trying to understand how BLAS and LAPACK in Fortran work and so on, so I made a code that generates a matrix and inverts it.
Here's the code
program test
Implicit none
external ZGETRF
external ZGETRI
integer ::M
complex*16,allocatable,dimension(:,:)::A
complex*16,allocatable,dimension(:)::WORK
integer,allocatable,dimension(:)::IPIV
integer i,j,info,error
Print*, 'Enter size of the matrix'
Read*, M
Print*, 'Enter file of the matrix'
READ(*,*), A
OPEN(UNIT=10,FILE = '(/A/)' ,STATUS='OLD',ACTION='READ')
allocate(A(M,M),WORK(M),IPIV(M),stat=error)
if (error.ne.0)then
print *,"error:not enough memory"
stop
end if
!definition of the test matrix A
do i=1,M
do j=1,M
if(j.eq.i)then
A(i,j)=(1,0)
else
A(i,j)=0
end if
end do
end do
call ZGETRF(M,M,A,M,IPIV,info)
if(info .eq. 0) then
write(*,*)"succeded"
else
write(*,*)"failed"
end if
call ZGETRI(M,A,M,IPIV,WORK,M,info)
if(info .eq. 0) then
write(*,*)"succeded"
else
write(*,*)"failed"
end if
deallocate(A,IPIV,WORK,stat=error)
if (error.ne.0)then
print *,"error:fail to release"
stop
end if
close (10)
end program test
The matrix A is in a file, which I'm calling, and also I say the size of the matrix (M ). When I copile them with gfortran I get these message
/tmp/ccVkb1zY.o: In function MAIN__':
test.f03:(.text+0x751): undefined reference tozgetrf_'
test.f03:(.text+0x85d): undefined reference to `zgetri_'
collect2: error: ld returned 1 exit status
I have installed BLAS and LAPACK installed so I don't know if I'm calling in a right way the library.
Any suggestion?

Answer 1

It looks like you might not have linked to the libraries. Try:
gfortran -o test test.f03 -llapack -lblas
This causes the linker (the program which joins all the program parts together; usually called "ld" on UNIX) to include the library code for the LAPACK call (or a dynamic link to it) in your program.
If the result of the above line is "cannot find -llapack" or similar, there are two common problems:
Libraries can be "shared" (names ending ".so") or "static" (names ending ".a"); the linker will look for the shared one, so if you only have the static one you should add "-static" before the library link:
gfortran -o test test.f03 -static -llapack -lblas
This will also make it look for the static version of BLAS; if you need the shared version, add "-shared" in front of the "-lblas":
gfortran -o test test.f03 -static -llapack -shared -lblas
You might find this page helpful.
The linker isn't looking in the right directory for the libraries. You need to locate the actual library (called something like "liblapack.so" or "liblapack.a") and make sure the directory it's in is included in the directories the linker looks in, e.g. to get it to look in "/mylibs/maths" as well:
gfortran -o test test.f03 -L/mylibs/maths -llapack -lblas