Introduction/Description

Bare-bones Fortran is our most universal computer language for computational physics. For general programming, however, it has been surpassed by C. Ratfor is Fortran with C-like syntax. Ratfor was invented by the people who invented C. After inventing C, they realized that they had made a mistake (too many semicolons) and they fixed it in Ratfor, although it was too late for C. Otherwise, Ratfor uses C-like syntax, the syntax that is also found in the popular languages C++ and Java .

At SEP we supplemented Ratfor77 by preprocessors to give Fortran77 the ability to allocate memory on the fly. These abilities are built into Fortran90 and are seamlessly included in Ratfor90. To take advantage of Fortran90's new features while maintaining the concise coding style provided by Ratfor required us to write a new Ratfor preprocessor, Ratfor90, which produces Fortran90, rather than Fortran77 code.

You should be able to read Ratfor if you already know Fortran or any similar computer language. Writing Ratfor is easy if you already know Fortran. In general written Fortran is valid Ratfor, the only. Ratfor uses C style definition of lines and {} for expanded statements. To maximize the amount of Ratfor, you will need to know its rules. Here they are:

Statements on a line may be separated by ";". Statements may be grouped together with braces "{ }". Do loops do not require statement numbers because "{ }" defines the range. Given that if( ) is true, the statements in the following { } are done. else{ } does what you expect. We may not contract else if to elseif. We may omit the braces { } where they contain only one statement. break (equivalent to the Fortran90 exit) causes premature termination of the enclosing { }. while( ) { } repeats the statements in { } while the condition ( ) is true. Ratfor recognizes a looping statement more general than do. It is for(initialize; condition; reinitialize){ }. repeat { ... } until( ) is a loop that tests at the bottom. next causes skipping to the end of any loop and a retrial of the test condition. next (equivalent to the Fortran90 cycle statement) is rarely used, and the Ratfor90 programer may write either next or cycle. With the cycle statement we encounter an inconsistency between Fortran and C-language. Where Ratfor uses next, the C-language uses continue (which in Ratfor and Fortran is merely a place holder for labels). The Fortran relational operators .gt., ge., .ne. , etc. may be written >, >=, !=, etc. The logical operators .and. and .or. may be written && and ||. Anything from a # to the end of the line is a comment. A line may be continued in Ratfor by ending it with the underscore charactor " _'' or Fortran90's &.

There are two rarely used features of Ratfor77 that were not implemented in Ratfor90. break 2 which escapes from {{ }}. This feature can easily be replaced by the loop naming features supported in Fortran90. Ratfor77 allows & and | for the logical operators && and ||. While attractive, it is not part of the C family of languages and we had to drop it because Fortran90 adopts & for line continuation.

Changing all the code that generated illustrations for four textbooks (of various ages) also turned up a few more issues: Fortran90 uses the words scale and matmul as intrinsics. Old Fortran77 programs using those words as variable names must be changed. Ratfor77 unwisely allowed variables of intrinsic (undeclared) types. We no longer allow this. Ratfor90 forces implicit none.

SEP has a considerable amount of legacy Ratfor77 code which used two home-grown preprocessors to get around Fortran77's memory allocation problems. Ratfor90 allows the conventions established by these preprocessors, interpreting them into standard Fortran90.

Memory allocation in subroutines

temporary real*4 data(n1,n2,n3), convolution(j+k-1)

These declarations must follow other declarations and precede the executable statements. Automatic arrays are supported in Fortran90. To allow full code compatibility Ratfor90 simply translates this statement to

Math funcion

Transient convolution

The main program environment

#  out.H
#
# Copy input to output and scale by scaleval
# keyword generic scale
#%
integer n1, n2, n3, esize
from history: integer n1, n2, n3, esize
if (esize !=4)  call erexit('esize != 4')
allocate: real x(n1,n2)

subroutine scaleit( n1,n2, x)
integer i1,i2, n1,n2
real  x(n1,n2), scaleval
from par: real scaleval=1.
call hclose()     # no more parameter handling.
call sreed('in', x, 4*n1*n2)
do i1=1,n1
        do i2=1,n2
                x(i1,i2) = x(i1,i2) * scaleval
call srite( 'out', x, 4*n1*n2)
return;        end

Downloading/Installing

Sample Output

#
#
# test.x
#%
program test{
integer i1,i2,n1,n2,count
real,pointer,dimension(:,:) :: input

from either: integer n1=5,n2=5
allocate(input(n1,n2))

input=0.; count=0

loop1: do i2=1,n2{
  for(i1=1; i1 <5 ; i1+=2){
    count++
    if(i1==3 && i2==4) break loop1
    else input(i1,i2) += count
  }
}
where(input == 0) input=-15.
write(0,*) input
}

!
!
!test.x
!%
program test
  integer i1,i2,n1,n2,count
  real,pointer,dimension(:,:) :: input
  integer fetch, putch
  call initpar()
  call doc('/homes/sep/bob/test.rs90')
  if (0==fetch('n1','d',n1))then
    n1=5
  end if
  if (0/=putch('From either: n1','d',n1))then
    call seperr('trouble writing n1 to history file')
  end if
  if (0==fetch('n2','d',n2))then
    n2=5
  end if
  if (0/=putch('From either: n2','d',n2))then
    call seperr('trouble writing n2 to history file')
  end if
  allocate(input(n1,n2))
  input=0.
  count=0
  loop1: do i2=1,n2
    i1=1
    do
      if( .not. (i1<5)) then
        exit
      end if
      count = count+1
    do
      if( .not. (i1<5)) then
        exit
      end if
      count = count+1
      if (i1 .eq. 3  .and. i2 .eq. 4)then
        exit loop1
      else
        input(i1,i2) = input(i1,i2) +  count
      end if
      i1=i1+2
    end do
  end do loop1
  where(input  .eq.  0)
    input=-15.
  end where
  write(0,*) input
end program