unknown floating point exception b8a1

Since I am not a good programmer, I spent a couple of hours to figure out, where is this error coming from without any results. Here is the error message: 'Floating point co-processir fault at address 00404244 in file at line 364'. This line is a function definition. I load a file in the beginning of my program. The code is working if the loaded file has 1000 Data points but if I load a file with 2000 Data points, I get this error. I declared the arrays and pre-assigned them with the size 4000, so it wouldnt be the problem. My code is very long I can not post it here. Please help me if you can nice Saturday Miriam

Posting some lines of code near to line 364 may help us to see the problem.

FUNCTION F1(A,B,C) IMPLICIT DOUBLE PRECISION (A-H,O-Z) F1=B/(A*C) (LIne 364) RETURN END

and here is the call of the function

   D1=F1(RAR,ETA2+(H*C2),E(J+1))
   D2=F2(RAR,(ETA1+(H*C1)),VZ(J+1),Q,PER,E(J+1))

Make sure that F1 and its arguments are all DOUBLE PRECISION at the point of call.

Make sure that A and C are not very small.

Use CHECKMATE whilst testing.

here is where and how I call F1 :

  FUNCTION RB(Q,E,VZ,R)
	  IMPLICIT DOUBLE PRECISION (A-H,O-Z)
	  DOUBLE PRECISION, DIMENSION (4000)::E,VZ,R
      DOUBLE PRECISION ETA1, ETA2,RAR, H, C1, C2
	  COMMON/BOB/L,BI,IMAX,RE,REST,REPHI,FM,PR,PSI1,C3,UINF,PER
C
	ETA1=1.0
	ETA2=0.0
C
C
C
          DO 20 J=1,IMAX-1
	   H=R(J+1)-R(J)
	   RAR=R(J)
C
	   IF(RAR.LT.1.0E-06) THEN
	    A1=0.0
	   ELSE
	    A1=F1(RAR,ETA2,E(J))
	   END IF
	   A2=F2(RAR,ETA1,VZ(J),Q,PER,E(J))
C
	   RAR=RAR+H/2.0
	   EEE=(E(J)+E(J+1))/2.0
	   VVV=(VZ(J)+VZ(J+1))/2.0
C
	   B1=F1(RAR,ETA2+(H*A2)/2.0,EEE)
	   B2=F2(RAR,(ETA1+(H*A1)/2.0),VVV,Q,PER,EEE)
	   C1=F1(RAR,ETA2+(H*B2)/2.0,EEE)
	   C2=F2(RAR,(ETA1+(H*B1)/2.0),VVV,Q,PER,EEE)
C
	   RAR=RAR+H/2.0
C
	   D1=F1(RAR,ETA2+(H*C2),E(J+1))
	   D2=F2(RAR,(ETA1+(H*C1)),VZ(J+1),Q,PER,E(J+1))
C
	   ETA1=ETA1+(H*(A1+2.0*B1+2.0*C1+D1))/6.0
	   ETA2=ETA2+(H*(A2+2.0*B2+2.0*C2+D2))/6.0
C
 20       CONTINUE
C
	RB=ETA1
C
        RETURN
	END

EVery thing is double precision. I dont get it 😦 P.S: A and C are very small, and it should be that way

Quoted from Miriam

P.S: A and C are very small, and it should be that way

Hi Miriam,

How small? If the product A*C on the denominator underflows, i.e. it becomes to small to represent you will get an error.

Can you post the values of A and C so we can check? Or you could try re-writing your function as F1=(B/A)/C which might help if B is small.

Also did you try compiling with Checkmate enabled as Paul suggested?

I compiled with Checkmate, but also with Debug and ReleaseNet, no one is really working. I am now so confused about the values of A and C.

Perhaps you can define a minimum divisor and test the product A*C in your function F1 like here:

if (AC) .lt. 10.D0tiny(1.D0) --> program stops

Regards - Wilfried

It appear to me that you should check the values of A*C. You could do this in Function RB by including

      subroutine check_AC (R,E,IMAX)
!
      real*8 R(*),e(*),   tiny,RAR,EEE
      integer*4 imax,     n_err, j
!
      n_err = 0          ! count of zero A*C 
      tiny  = 1.d-10     ! estimate of what is too small for calculation ??
      DO J=1,IMAX-1 
         RAR = R(J)
         EEE = E(J)
         if ( abs (RAR*EEE) < tiny) then 
            write (*,*) 'small A*C=', RAR*EEE,' at J=',j
            n_err = n_err+1 
         end if 
         RAR = (R(J)+R(J+1))/2.0 
         EEE = (E(J)+E(J+1))/2.0 
         if ( abs (RAR*EEE) < tiny) then 
            n_err = n_err+1 
            write (*,*) 'small A*C=', RAR*EEE,' at J=',j,'.5'
         end if 
      end do 
      if (n_err > 0) write (*,*) n_err,' too small values of A*C detected'
!
      end 

This could indicate how best to improve Function RB to cope with what is assumed to be unusual values in R or E.