How to install LAPACK and BLAS library on Linux

To install LAPACK and BLAS library on Ubuntu, just type :

sudo apt-get install liblapack-dev

This automatically installs the LAPACK and BLAS library.
In my computer, this library was installed in this address:  /usr/lib/lapack/

In order to use the lapack library to compile and run the code, one needs
to use the following command:

ifort ProgranmName.f90 -L /usr/lib/lapack/ -llapack


Another useful command to check the existence of subroutines and functions
in the LAPACK and BLAS library, we can use

readelf -s /usr/lib/lapack/liblapack.so.* | grep -i NameOfSubroutine

Useful links for more infos: Link1, Link2

26 - How to check an exisiting file in FORTRAN

The inquire command in FORTRAN will help us to see what is on disk, and what is currently attached to units in our code.
For checking whether a file is existing in the current directory (where our fortran code is there) or not
we need to use
inquire(file='file_name', exist=lexist)
where lexist is a logical variable. if it is .true. then the file is exisiting in the current directory!

We can also check whether a file has been opened in the code or not.
inquire(unit=11, opened=lopen)
or
inquire(file='file_name', opened=lopen)
if the file has been already opened, the logical variable lopen is .true. otherwise it is .false. . 

25 - generating random number in FORTRAN

In Fortran one can use 
real:: rnd
call random_number(rnd)  

to generate random numbers between [0,1]. But the problem is that if we reuses this peice of the code again, we will get exactly the same squence of random numbers. To produce a different sequece random number each time, the generator can be seede in a number of ways such as:

integer:: count, seed
real:: rnd
call system_clock(count)
seed=count
call random_seed(put=seed)
call random_number(rnd)

more infos can be found in this website.

24 - Counting number of lines in a file within FORTRAN code

If you want to determine the number of line in a given file within your FORTRAN code,
you can do this following nice trick!

program count_lines
   implicit none
   integer:: n
   character(len=60):: cmd
    cmd = "cat file_name.dat | grep '[^ ]' | wc -l > nlines.txt"
    call system(cmd)
    open(1,file='nlines.txt')
    read(1,*) n
    print*, "Number of lines are", n 
    cmd = 'rm nlines.txt'
    call system(cmd)
end program

This simple code, uses linux command to find the number of lines.
Notice that  cat file_name.dat | grep '[^ ]' | wc -l  returns the number of lines in a file with ignoting the blank lines.