Fortran's warning on a program for evaluating elliptic integrals - fortran

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.

Related

Compiling Legacy Fortran Code with (more) Modern Fortran Code

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.

Fortran is reading beyond endfile record

I'm trying to read some data from a file, and the endfile record detection is important to stop reading. However, depending of the array dimensions of the array used to read data, I cannot detect properly the endfile record and my Fortran program stops.
The program is below:
!integer, dimension(3) :: x ! line 1.1
!integer, dimension(3,10) :: x ! line 1.2
integer, dimension(10,3) :: ! line 1.3
integer :: status,i=1
character(len=100) :: error
open( 30, file='data.dat', status='old' )
do
print *,i
!read( 30, *, iostat=status, iomsg=error ) x ! line 2.1
!read( 30, *, iostat=status, iomsg=error ) x(:,i) ! line 2.2
read( 30, *, iostat=status, iomsg=error ) x(i,:) ! line 2.3
if ( status < 0 ) then print *,'EOF'
print *,'total of ',i-1,' lines read.'
exit
else if ( status > 0 ) then
print *,'error cod: ',status
print *,'error message: ', error
stop
else if ( status == 0 ) then
print *,'reading ok.'
i = i + 1
end if
end do
With 'data.dat' file been:
10 20 30
30 40 50
When lines 1.3 and 2.3 are uncommented the mentioned error appears:
error cod: 5008
error message: Read past ENDFILE record
However, using lines 1.1 and 2.1, or 1.2 and 2.2, the program works, detecting endfile record.
So, I would like some help on understanding why I cannot use lines 1.3 and 2.3 to read properly this file, since I'm giving the correct number of array elements for read command.
I'm using gfortran compiler, version 6.3.0.
EDIT: simpler example
the following produces a 5008 "Read past ENDFILE record" error:
implicit none
integer x(2,2),s
open(20,file='noexist')
read(20,*,iostat=s)x
write(*,*)s
end
if we make x a scalar or a one-d array ( any size ) we get the expected -1 EOF flag. It doesn't matter if the file actually doesn't exist or is empty. If the file contains some, but not enough, data its hard to make sense of which return value you might get.
I am not sure if I am expressing myself correctly but it has to do with the way fortran is reading and storing 2d-arrays. When you are using this notation: x(:,i), the column i is virtually expanded in-line and the items are read using this one line of code. In the other case where x(i,:) is used, the row i is read as if you called read multiple times.
You may use implied loops if you want to stick with a specific shape and size. For example you could use something like that:read( 30, *, iostat=status, iomsg=error ) (x(i,j), j=1,3)
In any case you should check that your data are stored properly (as expected at least) in variable x.
Please note this is only a guess. Remember that Fortran stores arrays in column major order. When gfortran compiles read() x(:,i), the 3 memory locations are next to each other so in the executable, it produces a single call to the operating system to read in 3 values from the file.
Now when read() x(i,:) is compiled, the three data elements x(i,1), x(i,2) and x(i,3) are not in contiguous memory. So I am guessing the executable actually has 3 read calls to the operating system. The first one would trap the EOF but the 2nd one gives you the read past end of file error.
UPDATE: I have confirmed that this does not occur with Intel's ifort. gfortran seems to have had a similar problem before: Bad IOSTAT values when readings NAMELISTs past EOF. Whether this is a bug or not is debatable. The code certainly looks like it should trap an EOF.

Rainflow algorithm - Fortran conversion to Matlab

I am trying to convert a Rainflow cycle counting algorithm which is in Fortran, which is a language I am not familiar with, into Matlab.
There is a ready made Rainflow I've downloaded for Matlab but that does not fit the requirements of my project so I'm trying to build one from scratch.
Here is the Fortran code:
INTEGER BUFFER (4096), INDEX, VALUE, RANGE, MEAN, X, Y
INDEX = 0
10 CONTINUE
call 'get next peak/valley', VALUE
INDEX = INDEX + 1
BUFFER (INDEX) = VALUE
20 CONTINUE
IF (INDEX.LT.3) THEN
not enough points to form a cycle
GOTO 10
ELSE
X = ABS (BUFFER(INDEX) - BUFFER(INDEX - 1))
Y = ABS (BUFFER(INDEX - 1) - BUFFER(INDEX - 2))
IF (X.GE.Y) THEN
c -- cycle has been closed
RANGE = Y
MEAN = (BUFFER(INDEX-1) + BUFFER(INDEX-2))/2
c -- remove the cycle
INDEX = INDEX - 2
BUFFER(INDEX) = BUFFER(INDEX+2)
c -- see if this value closes any more cycles
GOTO 20
ELSE
GOTO 10
END IF
END IF
I had downloaded f2matlab (a Fortran to Matlab converter) but it requires a Fortran compiler which I do not have.
The bits I don't really understand how I can convert are:
The call 'get next… line (is this an input()?)
The BUFFER(4096) etc (is this a bit large to be a matrix in matlab?)
The GOTO/CONTINUE structure.
What do they mean, in English (or Matlab)?
I have seen
How to translate fortran goto state to matlab
and
translating loop from Fortran to MATLAB
but they do not help me very much.
This
call 'get next peak/valley', VALUE
isn't (currently) syntactically valid Fortran and I'm not sure whether any compiler of yore would have understood it either. I guess that it means get a VALUE for use in the following bits of code.
INTEGER BUFFER (4096)
is a simple declaration that BUFFER is a vector of 4096 integers, nothing to scare Matlab in that volume of data.
Finally, GOTO is an unconditional jump and the number following it is the label of the line to jump to, so GOTO 10 means execute the line with label 10 next. It was fairly common in FORTRAN of the vintage you are showing us to jump to a CONTINUE statement which is, in this context, a no-operation, execution continues to the next line.
In another context, with DO loops CONTINUE would have marked the end of the block of code inside the scope of the loop and would have a subtly different effect.

Fortran 90 rank mismatch

I am quite new in Fortran, and just got the program from a PhD. It is used to count the number of beads in certain histograms. Here is the code:
program xrdf
implicit none
include 'currentconf.fi'
real drdf,rdf12(200)
real xni12, Zface
integer ibead,iconf,ii,io,i,j,k,linecount
integer mchains, iendbead, nstart
logical ifend
Zface=1.5
mchains=49
drdf=0.1
xni12=0.
io=10
nstart=12636
open(file='pcushion.tr.xmol',unit=io)
do i=1,200
rdf12(i)=0.0
end do
ifend=.false.
do iconf=1,1000000
! reading current frame
ii=iconf
call readconf(io,ii,linecount,ifend)
write(*,*)' conf ',iconf,' N=',n
if (ifend) go to 777
! if trajectory ended, exit loop
ibead=0
do i=1,mchains
iendbead=nstart+i*45
dz=abs(Zface-z(iendbead))
ii=int(dz/drdf)+1
rdf12(ii)=rdf12(ii)+1
xni12=xni12+1.0
end do
end do !iconf
777 write(*,*)' total ',iconf-1,' frames '
write(*,*)' r rho(z) '
do i=1,200
write(*,'(f10.4,e15.7)')(i-0.5)*drdf,rdf12(i)/xni12
end do
close(io)
stop
end
Because I really do not know which part is wrong, so I just past all the code here. When I compile this program, there comes an error:
i=int(dz/drdf)+1
1
Error: Incompatible ranks 0 and 1 in assignment at (1)
How can I edit the program to fix it?
I was able to reproduce your compiler error using a simple program. It seems likely that in
ii=int(dz/drdf)+1
you are trying to assign an array (maybe dz?) to an integer (ii).
integer ibead,iconf,ii,io,i,j,k,linecount
Compare the dimensions of ii (dimension is 1) with the dimensions of dz and drdf.
This is my program (compiled it using gfortran):
PROGRAM TEST
implicit none
integer dz(10),ii
real dy
dz=3
dy=2.0
ii=int(dz/dy)+1
END PROGRAM TEST
Using ifort the error message is more revealing:
error #6366: The shapes of the array expressions do not conform

Fortran - problem with double precision

I have a small program that read some data from binary file and stores it into normal (unformatted) files. Here is the source:
Program calki2e
IMPLICIT NONE
!
DOUBLE PRECISION VAL
INTEGER P,Q,R,S
INTEGER IREC2C
PARAMETER( IREC2C=15000)
INTEGER AND,RSHIFT,LABEL,IMBABS,NX,IB,NFT77
INTEGER IND
DIMENSION IND(IREC2C)
DOUBLE PRECISION XP
DIMENSION XP(IREC2C)
CHARACTER(LEN=12) :: FN77 = 'input08'
CONTINUE
NFT77=77
!----------------------------------------------------------------------
2 CONTINUE
c
open(unit=NFT77,file=FN77,STATUS='OLD',
+ACCESS='SEQUENTIAL',FORM='UNFORMATTED')
open(unit=13,file='calki2e.txt')
REWIND(77)
4100 continue
READ(77) NX,IND,XP
IMBABS=IABS(NX)
DO 100 IB=1,IMBABS
LABEL=IND(IB)
P= AND(RSHIFT(LABEL, 24),255)
Q= AND(RSHIFT(LABEL, 16),255)
R= AND(RSHIFT(LABEL, 8),255)
S= AND( LABEL ,255)
VAL=XP(ib)
IF(P.EQ. Q) VAL=VAL+VAL
IF(R .EQ. S) VAL=VAL+VAL
IF((P .EQ. R).AND.(Q .EQ. S)) VAL=VAL+VAL
write(13,*)P,Q,R,S,val
100 CONTINUE
IF (NX.GT.0) GOTO 4100
CRB
CLOSE(UNIT=NFT77)
!
END
When I compile it using gfortran I obtain double precision in output file but with g77 I get only single precision. What it wrong and how to change it?
Do you mean the "write (13, *) statement. This is "list directed" output. It is a convenience I/O with few rules -- what you get will depend upon the compiler -- it is best used for debugging and "quick and dirty" programs. To reliably get all the digits of double precision, change to a formatted output statement, specifying the number of digits that you need. (It is probably best to switch to gfortran anyway, as g77 is no longer under development.)
your numbers are double precision but you are printing them in free format. You have to specify an explicit format
If you want to keep your code F77, try something like
write(13,1000) P,Q,R,S,val
1000 format(1X,4I7,1X,1E14.10)
The "1X"s mean one space, "4I7" means four seven-width integers, and 1E14.10 means one fourteen-charater width scientific-notation real number with 10 significant digits. Feel free to mess around with the numbers to get it to look right.
This is a pretty good tutorial on the topic.
I would be tempted to set the format on your write statement to something explicit, rather than use * in write(13,*)P,Q,R,S,val.