Linking with LAPACK using gfortran on Fedora Linux - fortran

Question

I need some help regarding installation of LAPACK ( for Fortran 95) on a Fedora machine.
I am writing this post after having tried all answers posted to pertinent queries in this forum.
I tried two different options:
METHOD 1
I directly downloaded the lapack95.a library from here (http://www.netlib.org/lapack95/, file named lapack95_linux_redhat.tgz. After unzipping, I could get file lapack95.a
After looking for some answers on how to link and use libraries, I wrote a trial code and saved in file try.f90 and then did the following
gfortran -c try.f90
gfortran -o try try.o -L/(name of directory where lapack95.a
was present. I put it in the same directory
as try.f90)/ -llapack95
( The fortran file try.f90 and lapack95.a were in the same directory)
I got the following error:
/usr/bin/ld: cannot find -llapack95
collect2: error: ld returned 1 exit status
I searched on internet and found here (https://forums.fedoraforum.org/archive/index.php/t-248227.html) that we need to install lapack-devel.
I did that and had the same outcome.
Method 2
I also tried running the above command (in Method 1) but without space between / and -llapack95 , i.e. as :
gfortran -o try try.o -L/(name of directory where lapack95.a
was present I put it in the same directory
as try.f90)/-llapack95
and received the following error:
try.o: In function `MAIN__':
try.f90:(.text+0xdb): undefined reference to `sgesv_'
collect2: error: ld returned 1 exit status
Method 3
After having no success, I thought may it's not good idea to use the lapack95.a downloaded directly. I should build it from the original files.
I realized that may be I need to install lapack95 through proper means following which from the same link
http://www.netlib.org/lapack95
I downloaded the file lapack95.tgz and followed the instructions in readme file.( which said just to run make file in SRC)
I made some changes as :
FC1 = f95 -fixed to
FC1 = f95
and
OPTS0 = -u -V -dcfuns -dusty -ieee=full
to
OPTS0 = -u -V
( as suggested on https://www.reddit.com/r/linux4noobs/comments/7tgmb9/fortran_library_netlib_lapack95_installation_error/)
I expected that the library will be created in /usr/lib/ or usr/local/lib as LAPACK3 but couldn't find it.
Infact there was an error ( and thus could not have any .a file )
f95 -free -c -u -V - -I./../lapack95_modules f77_lapack_double.f90 f95: error: -E or -x required when input is from standard input make: *** [../make.inc:45: f77_lapack_double.o] Error 1
I am not sure if any of my method is fine.
I expected Method 1 to work as I am linking the library locally but failure in all 3 cases.
Kindly suggest.
Thanks

Answer 1

Lapack library is a very useful tool to conduct matrix operations in a fast way. On the linux machine, it is very simple to install lapack with the build-in tools: dnf/yum or apt-get [2]. On my Fedora desktop, installation is like this:
sudo dnf install lapack64-devel.x86_64
Here is a small example on how to use lapack lib. The source code is to solve linear equations as linear_eqs.f [3].
Program LinearEquations
c solving the matrix equation A*x=b using LAPACK
Implicit none
c declarations, notice single precision
Real*4 A(3,3), b(3)
integer i, j, pivot(3), ok
c define matrix A
A(1,1)=3.1
A(1,2)=1.3
A(1,3)=-5.7
A(2,1)=1.0
A(2,2)=-6.9
A(2,3)=5.8
A(3,1)=3.4
A(3,2)=7.2
A(3,3)=-8.8
c define vector b, make b a matrix and you can solve multiple
c equations with the same A but different b
b(1)=-1.3
b(2)=-0.1
b(3)=1.8
c find the solution using the LAPACK routine SGESV
call SGESV(3, 1, A, 3, pivot, b, 3, ok)
c
c parameters in the order as they appear in the function call
c order of matrix A, number of right hand sides (b), matrix A,
c leading dimension of A, array that records pivoting,
c result vector b on entry, x on exit, leading dimension of b
c return value
c
c print the vector x
do i=1, 3
write(*,*) b(i)
end do
end
In this code, one lapack function 'sgesv()' is used. To execute this file, run the below command:
gfortran linear_eqs.f -llapack -o lineqs.out
./lineqs.out
The outputs will be:
1.00000024
1.00000036
1.00000036
Reference
[1] https://github.com/fxcoudert/gfortran-for-macOS/releases
[2] BLAS, ATLAS, LAPACK Shared library minimal example
[3] http://physics.oregonstate.edu/~landaur/nacphy/lapack/codes/linear-f.html