Best way to write a large array to file in fortran? Text vs Other

Question

I wanted to know what the best way to write a large fortran array ( 5000 x 5000 real single precision numbers) to a file. I am trying to save the results of a numerical calc

Answer 1

OPEN the file for reading and writing as "unformatted", and READ and WRITE the data without supplying a format, as demonstrated in the program below.

program xunformatted
integer, parameter :: n = 5000, inu = 20, outu = 21
real               :: x(n,n)
integer            :: i
character (len=*), parameter :: out_file = "temp_num"
call random_seed()
call random_number(x)
open (unit=outu,form="unformatted",file=out_file,action="write")
do i=1,n
   write (outu) x(i,:) ! write one row at a time
end do
print*,"sum(x) =",sum(x)
close (outu)
open (unit=inu,form="unformatted",file=out_file,action="read")
x = 0.0
do i=1,n
   read (inu) x(i,:)   ! read one row at a time
end do
print*,"sum(x) =",sum(x)
end program xunformatted