Error in linking gfortran to LAPACK and BLAS

Question

I have installed LAPACK and BLAS from Synaptic package manager in Ubuntu.

whereis libblas
libblas: /usr/lib/libblas.so /usr/lib/libblas.a /usr/lib/libblas

whereis liblapack
liblapack: /usr/lib/liblapack.a /usr/lib/liblapack.so

When I try to compile the randomsys1 example with gfortran I get the following error messages.

gfortran randomsys1.f90 -L/usr/lib/lapack -llapack -L/usr/lib/libblas -lblas
/tmp/cclwtifh.o: In function `MAIN__':
randomsys1.f90:(.text+0x12): undefined reference to `init_random_seed_'
collect2: error: ld returned 1 exit status

or

gfortran randomsys1.f90 -llapack -lblas
/tmp/ccB1isEC.o: In function `MAIN__':
randomsys1.f90:(.text+0x12): undefined reference to `init_random_seed_'
collect2: error: ld returned 1 exit status

As per my understanding, it is the recommended way to link gfortran with lapack and blas (kindly refer to gfortran LAPACK “undefined reference” error). Thanks in advance for pointing out the correct way to compile the fortran code using gfortran.

Answer 1

Give this a try

gfortran randomsys1.f90 -L/usr/lib -llapack -L/usr/lib -lblas

I think you went one directory too far

I wrote a program using the LAPACK eigensolver and here is how I successfully compiled it on my own computer. It was used to calculate modes of a spring-mass system.

gfortran eigen.f90 -L/usr/local/lib -lblas -L/usr/local/lib -llapack

This also works on my computer

gfortran eigen.f90 -lblas -llapack

I just tried both to verify.

PS, now that you know how to compile, I think you need the subroutine init_random_seed in your program (goes after "contains" but before "end program"). This one is from google. No idea if it is what you need, your professor should be able to steer you correctly here.

! Initialize the random number generator using current time,
! so a new sequence of random numbers is generated each 
! execution time.

! Taken from http://gcc.gnu.org/onlinedocs/gfortran/RANDOM_005fSEED.html

    SUBROUTINE init_random_seed()
        INTEGER :: i, n, clock
        INTEGER, DIMENSION(:), ALLOCATABLE :: seed

        CALL RANDOM_SEED(size = n)
        ALLOCATE(seed(n))

        CALL SYSTEM_CLOCK(COUNT=clock)

        seed = clock + 37 * (/ (i - 1, i = 1, n) /)
        CALL RANDOM_SEED(PUT = seed)

        print *, "Using random seed = ", seed
        print *, " "

        DEALLOCATE(seed)
    END SUBROUTINE