program test
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c      This program is a collection of frequently used fortran         c
c      commands. You need an input file 'numbers.dat' with 7 lines     c
c      and 2 number entries in each line. Check the output in          c
c      'maxed.dat' . You also need the header-file named 'declar.fh' . c
c                                                                      c
c                                     Elsebeth Schroder March 14, 2000 c
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c23456789012345678901234567890123456789012345678901234567890123456789012
c
c      A character in the first position of a line makes the compiler
c      ignore the line. A character in the 6th position is a code
c      to tell the compiler that the line is a continuation of the
c      previous line. You can number a line (for use with "goto")
c      using the 2nd to 5th character. However, goto-commands othen
c      lead to bad programming, and the command can most of the time
c      be avoided by using instead slightly non-standard commands.
c      All modern compilers will understand these commands, and
c      I use them in this sample program.
c
c      You can write your commands from position 8 to 72. Anything
c      at position 73 and onwards is ignored by the compiler.
c      
       implicit none
c
c      In Fortran you do not have to declare all your variables; 
c      they are implicitly declared depending on the starting letter
c      in their name. This is dangerous: if you misspell a variable
c      name you suddenly calculate something different than what you
c      think. For this reason, I always turn off the implicit 
c      variable declaration using the command "implicit none".
c      Now the compiler will complain if you forgot to declare
c      a variable or misspelled its name.
c
       include 'declar.fh'
c
c      If you put declarations that are also used in functions/subroutines
c      in a separate file you will only need to change e.g. the maximum
c      numbers of rows (max_iy) in the header file, not in every
c      function/subroutine declaration.
c
       call myread(tabel)
c
       do iy=1,max_iy
          tabel(1,iy)=mymax(tabel(1,iy),tabel(2,iy))
          tabel(2,iy)=tabel(1,iy)
       enddo
c
       call mywrite(tabel)
c
       stop
       end
c
c      This ends the main program. Below are the functions and 
c      subroutines. They can also be saved in external files, one
c      file for each procedure/subroutine. With separate files more
c      than one person at a time can edit the program, provided that
c      the changes are consistent with the rest of the program.
c
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c
c
       function mymax(value1,value2)
c
c      This function simply finds the maximum value of two numbers.
c      This is only meant as an example of the use of "function", 
c      "if" etc. There already exists a similar function in
c      Fortran, "max".
c
       implicit none
       include 'declar.fh'
       real*8 value1, value2
c       
       if (value1.gt.value2) then
          mymax=value1
       else
          mymax=value2
       endif
       end
c
c      The commonly used relational operators are
c      .gt.  corresponds to  >  (greater than)
c      .ge.  corresponds to  >=  (greater than or equal)
c      .lt.  corresponds to  <  (less than)
c      .le.  corresponds to  <=  (less than or equal)   
c      .eq.  corresponds to  =  (equal to) 
c      .and.
c      .or.  inclusive or (this or that or both)
c      .nor. exclusive or (this or that but not both)
c     
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c
       subroutine myread(tabel)
c
       implicit none
       include 'declar.fh'
c
       open(unit=1,file='numbers.dat',type='old')
       do iy=1,max_iy
          read(1,*) tabel(1,iy),tabel(2,iy)
       enddo
       close(1)
       end
c
c      units 5 and 6 are reserved for standard input and standard
c      output (often: keyboard and screen). You will get strange results
c      if you try to use unit 5 or 6 for files.
c
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c
       subroutine mywrite(tabel)
c
       implicit none
       include 'declar.fh'
c
       open(unit=2,file='maxed.dat',type='unknown')
       do iy=1,max_iy
          write(2,*) real(tabel(1,iy)),real(tabel(2,iy))
       enddo
       close(2)
c       
       end