Compiling Legacy Fortran Code with (more) Modern Fortran Code - fortran

I have been working with some old legacy code in Fortran used by a colleague. The actual code is proprietary, so the examples I use here are abbreviated compared to the code I'm working with.
Some of the procedures individually defined in *.f files included a file called variables.h:
Example contents of variables.h:
c VARIABLE DIMENSIONS FOR MODEL
c height_dim -- number of vertical (z) steps
c length_dim -- number of horizontal (x) steps
c width_dim -- number of horizontal (y) steps
INTEGER height_dim, length_dim, width_dim, nmodes, styleFlag
PARAMETER (height_dim=80, length_dim=50, width_dim=40)
PARAMETER (nmodes = 4,
$ styleFlag = 3)
I changed that to the following:
! VARIABLE DIMENSIONS FOR MODEL
! height_dim -- number of vertical (z) steps
! length_dim -- number of horizontal (x) steps
! width_dim -- number of horizontal (y) steps
INTEGER height_dim, length_dim, width_dim, nmodes, styleFlag
PARAMETER (height_dim=80, length_dim=50, width_dim=40)
PARAMETER (nmodes = 4, styleFlag = 3)
An example routine that uses these might be the following, called initial_conditions.f:
c This sets up the PDE's initial conditions
subroutine initial_conditions( temperature, density )
IMPLICIT NONE
INCLUDE 'variables.h'
real*8 temperature(height_dim,length_dim,width_dim)
real*8 density(height_dim)
temperature = 273.15D0
density = 1.0D0
return
end
I tried to compile a test routine written in F90 (or newer?) that included dimensions.h, but the compiler didn't like the fixed-form comments being included into the free-form *.f90 source file, so I changed all comments from c to !. Then I was able to compile my test program successfully. Let's call it test.f90:
program test
implicit none
include 'variables.h'
real*8, dimension(height_dim,length_dim,width_dim) :: vx, vy, vz
! <<Initialize data...>>
! << Output data...>>
end program test
Unfortunately, now the original code doesn't compile. It seems that code doesn't like commented lines to begin with ! (based on the fact that that was all I changed), but the actual errors it gives are the following:
variables.h(8): error #5082: Syntax error, found END-OF-STATEMENT when expecting one of: =
PARAMETER (nmodes = 4, styleFlag = 3)
------------------------------------------^
variables.h(5): error #6219: This variable, used in a specification expression, must be a dummy argument, a COMMON block object, or an object accessible through host or use association. [NMODES]
INTEGER height_dim, length_dim, width_dim, nmodes, styleFlag
---------------------------------------------^
What in the world is going on, and how can it be fixed?!
I imagine that comment styles are incompatible (free-form fortran thinks c is a variable, not a comment?), but I have no idea how it would produce these errors.

Related

How to compile a Fortran subroutine

I have a small fortran subroutine that I got from here: How to call a Fortran program from R I saved it on C:\Fortran\horner.f90, however, when I try compile it using the command line I get an error saying that R is not recognized. See screenshots below. I do have Rtools installed and on my PATH. Am I missing something? Thanks for any pointers.
And this is the error I get:
Here is the horner.f90 file as well:
subroutine horner(n, a, x, y)
implicit none
integer :: n, i
double precision :: a(n), x, y
y = a(n)
do i = n - 1, 1, -1
y = y * x + a(i)
end do
end subroutine
UPDATE:
Here is a screenshot of where my R icon properties look like:
In the "Edit environment variable" window, it should be one entry per path, and not several paths separated by a ;.
This window was enhanced in Windows 10, in previous versions of Windows you had to type everything as one line, managing the ; separator yourself. But this no longer holds.
When you type, say C:\a;C:\b as one entry here, then in a command line the path will have ...;"C:\a;C:\b", that is it will consider "C:\a;C:\b" as one single string describing a path, which is of course wrong, and the Console won't find anything in these directories.

How to handle an optional group in a Fortran Namelist

I am working with a code originally written in Fortran 77 that makes use of namelists (supported by compiler extension at the time of its writing - this feature only became standard in Fortran 90) for reading input files. The namelist input files have groups of namelist variables in between (multiple) plain text headers and footers (see example.nml). Some groups of namelist variables are only read if certain conditions are met for previously read variables.
When reading all the namelist groups in a file in sequence, executables compiled with gfortran, ifort and nagfor all behave the same and give the expected output. However, when a given namelist group in the input file is to be skipped (the optional reading), gfortran and ifort executables handle this as desired, while the executable compiled with nagfor raises a runtime error:
Runtime Error: reader.f90, line 27: Expected NAMELIST group /GRP3/ but found /GRP2/
Program terminated by I/O error on unit 15 (File="example.nml",Formatted,Sequential)
As a minimal working example reproducing the problem, consider the namelist file example.nml and driver program reader.f90 given below, in which NUM2 from namelist group GRP2 should only be read if NUM1 from namelist group GRP1 equals 1:
example.nml:
this is a header
&GRP1 NUM1=1 /
&GRP2 NUM2=2 /
&GRP3 NUM3=3 /
this is a footer
reader.f90:
program reader
implicit none
character(len=40) :: hdr, ftr
integer :: num1, num2, num3, icode
! namelist definition
namelist/grp1/num1
namelist/grp2/num2
namelist/grp3/num3
! open input file
open(unit=15, file='example.nml', form='formatted', status='old', iostat=icode)
! read input data from namelists
read(15, '(a)') hdr
print *, hdr
read(15, grp1)
print *, num1
if (num1 == 1) then
read(15, grp2)
print *, num2
end if
read(15,grp3)
print *, num3
read(15, '(a)') ftr
print *, ftr
! close input file
close(unit=15)
end program reader
All executables give this expected output when NUM1=1:
this is a header
1
2
3
this is a footer
However, when e.g. NUM1=0, the executables compiled with gfortran and ifort give the desired output:
this is a header
0
3
this is a footer
while the executable compiled with nagfor (which is known for being strictly standard conforming), reads the header and first namelist group:
this is a header
0
but then terminates with the previously mentioned runtime error.
As indicated by the error message, example.nml is accessed sequentially, and if that is the case, /GRP2/ is the next record to be read, not /GRP3/ as the program logic asks for, so the error message makes sense to me.
So my question is this:
Can the shown behaviour be attributed to standard (non-)conformance enforced by nagfor and not gfortran and ifort?
If so, does this mean that the non-sequential reading observed with gfortran and ifort is due to extensions supported by these compilers (and not nagfor)? Can this be turned on/off using compiler flags?
The simplest workaround I can think of (minimal change to a large existing program), would be to add a dummy read(15,*) in an else branch for the if statement in reader.f90. This seems to work with all the mentioned compilers. Would this make the code standard conforming (Fortran 90 or later)?
These are the compiler versions and options that were used to compile the executables:
GNU Fortran (Ubuntu 9.1.0-2ubuntu2~18.04) 9.1.0:
gfortran -Wall -Wextra -fcheck=all -g -Og -fbacktrace reader.f90
Intel(R) Visual Fortran, Version 16.0 Build 20160415:
ifort -Od -debug:all -check:all -traceback reader.f90
NAG Fortran Compiler Release 6.1(Tozai) Build 6116:
nagfor -O0 -g -C reader.f90
When namelist formatting is requested on an external file, the namelist record is taken to commence at the record at the current position of the file.
The structure of a namelist input record is well defined by the language specification (see Fortran 2018 13.11.3.1, for example). In particular, this does not allow a mismatching namelist group name. nagfor complaining about this does so legitimately.
Several compilers do indeed appear to continue skipping over records until the namelist group is identified in a record, but I'm not aware of compiler flags available to control that behaviour. Historically, the case was generally that multiple namelists would be specified using distinct files.
Coming to your "simple workaround": this is, alas, not sufficient in the general case. Namelist input may consume several records of an external file. read(15,*) will advance the file position by only a single record. You will want to advance to after the terminating record for the namelist.
When you know the namelist is just that single record then the workaround is good.
#francescalus' answer and comment on that answer, clearly explained the first two parts of my question, while pointing out a flaw in the third part. In the hope that it may be useful to others that stumble upon a similar problem with a legacy code, here is the workaround I ended up implementing:
In essence, the solution is to ensure that the file record marker is always positioned correctly before attempting any namelist group read. This positioning is done in a subroutine that rewinds an input file, reads through records until it finds one with a matching group name (if not found, an error/warning can be raised) and then rewinds and repositions the file record marker to be ready for a namelist read.
subroutine position_at_nml_group(iunit, nml_group, status)
integer, intent(in) :: iunit
character(len=*), intent(in) :: nml_group
integer, intent(out) :: status
character(len=40) :: file_str
character(len=:), allocatable :: test_str
integer :: i, n
! rewind file
rewind(iunit)
! define test string, i.e. namelist group we're looking for
test_str = '&' // trim(adjustl(nml_group))
! search for the record containing the namelist group we're looking for
n = 0
do
read(iunit, '(a)', iostat=status) file_str
if (status /= 0) then
exit ! e.g. end of file
else
if (index(adjustl(file_str), test_str) == 1) then
! backspace(iunit) ?
exit ! i.e. found record we're looking for
end if
end if
n = n + 1 ! increment record counter
end do
! can possibly replace this section with "backspace(iunit)" after a
! successful string compare, but not sure that's legal for namelist records
! thus, the following:
if (status == 0) then
rewind(iunit)
do i = 1, n
read(iunit, '(a)')
end do
end if
end subroutine position_at_nml_group
Now, before reading any (possibly optional) namelist group, the file is positioned correctly first:
program new_reader
implicit none
character(len=40) :: line
integer :: num1, num2, num3, icode
! namelist definitions
namelist/grp1/num1
namelist/grp2/num2
namelist/grp3/num3
! open input file
open(unit=15, file='example.nml', access='sequential', &
form='formatted', status='old', iostat=icode)
read(15, '(a)') line
print *, line
call position_at_nml_group(15, 'GRP1', icode)
if (icode == 0) then
read(15, grp1)
print *, num1
end if
if (num1 == 1) then
call position_at_nml_group(15, 'GRP2', icode)
if (icode == 0) then
read(15, grp2)
print *, num2
end if
end if
call position_at_nml_group(15, 'GRP3', icode)
if (icode == 0) then
read(15, grp3)
print *, num3
end if
read(15, '(a)') line
print *, line
! close input file
close(unit=15)
contains
include 'position_at_nml_group.f90'
end program new_reader
Using this approach eliminates uncertainty in how different compilers treat not finding matching namelist groups at the current record in a file, generating the desired output for all compilers tested (nagfor, gfortran, ifort).
Note: For brevity, only a bare minimum of error checking is done in the code snippet shown here, this (and case insensitive string comparison!) should probably be added.

Error in fortran, undefined reference to subroutine

I am writing a subroutine and main function to call it, but getting error as undefined reference to ___. I found one reason: When I save the main and subroutine in the same file, compile and run that file, everything runs perfectly. However, when I save them into different .f90 files and try to run the main file, I get error. Is there any way I can make subroutine into a separate file and call into main calling program?
I got confused with another place - in the main program at !------ERROR------ place. I referred to Automatic width integer descriptor in fortran 90 I can use I0 as automatic width display indicator. But when I used the same, there is run time error expected integer but got character. Any idea about this?
! saved as sub_program.f90 file
SUBROUTINE sub_program (v1,v2,ctr)
IMPLICIT NONE
INTEGER, INTENT(IN) :: ctr
INTEGER, INTENT (OUT) :: v1,v2
SELECT CASE (ctr)
CASE (1)
v1=1
v2=0
CASE (2)
v1=0
v2=1
END SELECT
RETURN
END SUBROUTINE
! main calling program, saved as caller.f90
PROGRAM caller
IMPLICIT NONE
INTEGER :: v1,v2,ctr
DO ctr = 1,2,1
CALL sub_program (v1,v2,ctr)
WRITE (*,100) 'STEP = ',ctr,'V1 = ',v1,'V2 = ',v2 !------ERROR------
100 FORMAT (I0)
END DO
END PROGRAM
Thanks!
What is your compile command? For me, this compiles and runs normally
gfortran caller.f90 foo.f90 && ./a.out
I0 is an integer indicator, but some items following your WRITE statement are character strings. You can try, for example,
100 FORMAT (3(A, I0, 1X))
where 1X refers to a space.
As a note, if formatting is not terribly important and you're only interested in seeing some quick results, you can use the free format output (WRITE(*,*) ...).
EDIT: I had incorrectly referred to FORMAT as obsolete.

Fortran's warning on a program for evaluating elliptic integrals

On internet, I found this program that demonstrate Evaluating elliptic integrals of first and second kinds (complete)
implicit none
real*8 e,e1,e2,xk
integer i, n
e=1.d-7
print *,' K K(K) E(K) STEPS '
print *,'------------------------------------------'
xk=0.d0
do i = 1, 20
call CElliptic(e,xk,e1,e2,n)
write(*,50) xk,e1,e2,n
xk = xk + 0.05d0
end do
print *,'1.00 INFINITY 1.0000000 0'
stop
50 format(' ',f4.2,' ',f9.7,' ',f9.7,' ',i2)
end
Complete elliptic integral of the first and second kind. The input parameter is xk, which should be between 0 and 1. Technique uses Gauss' formula for the arithmogeometrical mean. e is a measure of the convergence accuracy. The returned values are e1, the elliptic integral of the first kind, and e2, the elliptic integral of the second kind.
Subroutine CElliptic(e,xk,e1,e2,n)
! Label: et
real*8 e,xk,e1,e2,pi
real*8 A(0:99), B(0:99)
integer j,m,n
pi = 4.d0*datan(1.d0)
A(0)=1.d0+xk ; B(0)=1.d0-xk
n=0
if (xk < 0.d0) return
if (xk > 1.d0) return
if (e <= 0.d0) return
et n = n + 1
! Generate improved values
A(n)=(A(n-1)+B(n-1))/2.d0
B(n)=dsqrt(A(n-1)*B(n-1))
if (dabs(A(n)-B(n)) > e) goto et
e1=pi/2.d0/A(n)
e2=2.d0
m=1
do j = 1, n
e2=e2-m*(A(j)*A(j)-B(j)*B(j))
m=m*2
end do
e2 = e2*e1/2.d0
return
end
I have compiled it but I have received the following errors:
gfortran -Wall -c "gauss.f" (nel direttorio: /home/pierluigi/Scrivania)
gauss.f:53.9:
50 format(' ',f4.2,' ',f9.7,' ',f9.7,' ',i2)
1
Error: Invalid character in name at (1)
gauss.f:83.72:
if (dabs(A(n)-B(n)) > e) goto et
1
Warning: Deleted feature: Assigned GOTO statement at (1)
gauss.f:83.35:
if (dabs(A(n)-B(n)) > e) goto et
1
Error: ASSIGNED GOTO statement at (1) requires an INTEGER variable
gauss.f:48.18:
write(*,50) xk,e1,e2,n
1
Error: FORMAT label 50 at (1) not defined
Compilation failed.
Any suggestions please?
EDIT
I have read all your answers and thanks to you I managed to compile the program. I also have another curiosity and I do not know whether to write another question. In the meantime I modify this question. In my program, xk is increased by 0.05. Now I will that the program to read data from a file containing: the minimum value of xk; the maximum value of xk; the number of intervals. I thought:
open (10,file='data/test')
read (10,*) xkmi, xkma
read (10,*) nk
close (10)
lkmi = dlog(xkmi)
lkma = dlog(xkma)
ldk = (lkma-lkmi)/dfloat(nk-1)
In addition, the program must be modified in such a way that the result is written to another file. How can I change the rest of the program? Thank you very much.
Your source code file extension is f which, I think (check the documentation), tells gfortran that the file contains fixed source form. Until Fortran 90 Fortran was still written as if onto punched cards and the location of various bits and pieces of a line is confined to certain columns. A statement label, such as 50 in the first of the error messages, had to be in columns 1 - 6. Two solutions:
Make sure the label is in (some of) those columns. Or, better
Move to free source form, perhaps by changing the file extension to f90, perhaps by using a compilation option (check your documentation).
The error raised by the goto et phrase is, as your compiler has told you, an example of a deleted feature, in which the goto jumps to a statement whose label is provided at run-time, ie the value of et. Either tell your compiler (check ...) to conform to an old standard, or modernise your source.
Fix those errors and, I suspect, the other error messages will disappear. They are probably raised as a consequence of the compiler not correctly parsing the source after the errors.
Because the file has type ".f" gfortan is interpreting it as fixed-source layout. Trying compiling with the free-form layout by using compiler option -ffree-form and see if that works. This probably explains the error about the "invalid character". That statement not being recognized explains the "format not defined error". The "computed goto" is obsolete but valid Fortran. You can ignore that warning. If you wish, later you can modernize the code. For the remaining error, for the "assigned goto", declare "et" as an integer.
I would just do this
10 n = n + 1
! Generate improved values
A(n)=(A(n-1)+B(n-1))/2.d0
B(n)=dsqrt(A(n-1)*B(n-1))
if (dabs(A(n)-B(n)) > e) goto 10
and possibly compile as free form source as others have shown. The label et seems weird and non-standard, possibly a rare vendor extension.
You could also change the lines above to a do-loop with an exit statement (Fortran 90).
(The program compiled for me after the change).
I tested the subroutine and compared with matlab and it was not the same. It is very similar to the algorithm used in Abramowitz's book. Here is the one I wrote that works well, just for comparing.
subroutine CElliptic(m,K,E)
implicit none
real*8 m,alpha,E,K,A,B,C,A_p,B_p,C_0,pi,suma
integer j,N
N=100
alpha=asin(sqrt(m))
pi = 4.d0*datan(1.d0)
A_p=1.0
B_p=cos(alpha)
C_0=sin(alpha)
suma=0.0
do j=1,N
A=(A_p+B_p)/2.0d0
B=dsqrt(A_p*B_p)
C=(A_p-B_p)/2.0d0
suma=suma+2**(j)*C**2
A_p=A
B_p=B
end do
K=pi/(2*A)
E=(1-1.d0/2.d0*(C_0**2+suma))*K
end Subroutine CElliptic
best regards
Ed.

Fortran subroutine hung up on OPEN statement

I've recently started working on an existing Fortran program, and picking up the language at the same time. I wrote the following subroutine:
subroutine timing(yyyy, mm, dd, var, ntime, time_blocks,
* time_day)
use myglobals
! ---------------------------------------------------------------------
! Common Variables
! ---------------------------------------------------------------------
integer yyyy, ! year
* mm, ! month
* dd, ! day
* ntime ! nr of blocks for which time was measured
real time_blocks(ntime),
* time_day
character*4 var
! ---------------------------------------------------------------------
! Internal Variables
! ---------------------------------------------------------------------
integer ios
integer out_unit=52
open(unit=out_unit, file=diroutput(1:69)//'timing',
* err=450, iostat=ios)
450 print*, "iostat= ", iostat
print*, "open"
write(out_unit, format_str) yyyy, mm, dd, var, time_blocks,
* time_day
return
end
The purpose of this subroutine is to write the inputs it gets from another part of the program to a file, following a defined format (format definition not included in my example). The file must be created on the first call of this subroutine, then accessed on each further call in order to append the new information. diroutput is a character string defined in myglobals.
My problem is that the program seems to get hung up at the OPEN statement, i.e. nothing happens until I kill the process. I ran the code with several print*, statements to locate the error, and found out this way that the error must be in the OPEN statement. It seems strange that the program does nothing at all, not even jump to the error label.
As I'm new to Fortran I might be missing something fairly obvious, so a quick look by someone more experienced might help. I'm certain that diroutput contains a valid path.
I'm using Linux (CentOS 5.5) and I compiled my program with Intel Fortran Compiler 11.1.
Your code seems, from the continuation characters in (generally) column 6, to be written in fixed-form despite containing features of Fortran 90. If it is fixed-form then statement labels, such as 450 should be in columns 1 to 5. I don't immediately see why that would cause the program to hang rather than crash, but I suggest you fix this and try again.