error #6366: The shapes of the array expressions do not conform

Question

I create a program to solve two-body problem by runge-kutt method. I was faced with the problem: when I call the function which return the ELEMENT of two-dimension array from expression, which must give the ELEMENT of two-dimension array too (sorry for confusion with terms), I get this message:

 error #6366: The shapes of the array expressions do not conform.
[X1]
      X1(DIM,i)=X1(DIM,i-1)+0.5D0*ABS(i/2)*H*K1(DIM,i-1,X1(DIM,i-1),X2(DIM,i-1),V1(DIM,i-1),V2(DIM,i-1),NDIM,ORD,2,maxnu)

I have a external interface for this function and it's apparently that compiler consider this as a function.

I must clarify some things:

Yes, it's not quite Fortran, it's preprocessor Trefor, which is used by astronomers in Moscow University (I'm just a student). This language is very similar to fortran, but a bit closer to C (Semi-colons for example), which is studied by many students. Runge-Kutta method can be briefly written as: We have initial value problem

dy/dt=f(t,y),   y(t0)=y0

y is unknown vector, which contains 12 components in my case (3 coordinates and 3 velocities for each body)

next step is

y(n+1)=y(n)+1/6*h*(k1+2k2+2k3+k4), t(n+1)=t(n)+h
where
k1=f(tn,yn),
k2=f(tn+1/2h,yn+h/2*k1)
k3=f(tn+1/2h,yn+h/2*k2)
k4=f(tn+1/2h,yn+k3)

Ie in my code X1,2 and V1,2 and K_1,2 should be vectors, because each of them must be have 3 spatial components and 4 components for each 'order' of method. The full code:

FUNCTION K1(DIM,i,X1,X2,V1,V2,NDIM,ORD,nu,maxnu)RESULT (K_1);
        integer,intent(in) :: i,DIM,nu;
        real(8) :: K_1;
        real(8) :: B1;
        real(8) :: R;
        real(8),intent(in) :: X1,X2,V1,V2;
COMMON/A/M1,M2,Fgauss,H;
        integer,intent(in) :: NDIM,ORD,maxnu;
Dimension :: B1(NDIM, ORD);
Dimension :: X1(NDIM,ORD),X2(NDIM,ORD),V1(NDIM,ORD),V2(NDIM,ORD);
Dimension :: K_1(NDIM,ORD);
   IF (nu>=2) THEN;
B1(DIM,i)=V1(DIM,i);
ELSE;
R=((X1(1,i)-X2(1,i))**2.D0+(X1(2,i)-X2(2,i))**2.D0+(X1(3,i)-X2(3,i))**2.D0)**0.5D0;
B1(DIM,i)=Fgauss*M2*(X2(DIM,i)-X1(DIM,i))/((R)**3.D0);
   END IF;
K_1(DIM,i)=B1(DIM,i);
      RETURN;
     END FUNCTION K1;

 FUNCTION K2(DIM,i,X1,X2,V1,V2,NDIM,ORD,nu,maxnu)RESULT (K_2);
        integer,intent(in) :: i,DIM,nu;
        real(8) :: K_2;
        real(8) :: B2;
        real(8) :: R;
        real(8),intent(in) :: X1,X2,V1,V2;
COMMON/A/M1,M2,Fgauss,H;
        integer,intent(in) :: NDIM,ORD,maxnu;
Dimension :: B2(NDIM,ORD);
Dimension :: X1(NDIM,ORD),X2(NDIM,ORD),V1(NDIM,ORD),V2(NDIM,ORD);
Dimension :: K_2(NDIM,ORD);
   IF (nu>=2) THEN;
B2(DIM, i)=V2(DIM,i);
ELSE;
R=((X1(1,i)-X2(1,i))**2.D0+(X1(2,i)-X2(2,i))**2.D0+(X1(3,i)-X2(3,i))**2.D0)**0.5D0;
B2(DIM, i)=Fgauss*M1*(X2(DIM,i)-X1(DIM,i))/((R)**3.D0);
   END IF;
K_2(DIM,i)=B2(DIM, i);
      RETURN;
        END FUNCTION K2;

 PROGRAM RUNGEKUTT;
   IMPLICIT NONE;
   Character*80 STRING;
real(8) :: M1,M2,Fgauss,H;
real(8) :: R,X1,X2,V1,V2;
 integer :: N,i,DIM,NDIM,maxnu,ORD;
 integer :: nu;
 PARAMETER(NDIM=3,ORD=4,maxnu=2);
   Dimension :: X1(NDIM,ORD),X2(NDIM,ORD);
   Dimension :: V1(NDIM,ORD),V2(NDIM,ORD);
INTERFACE;
    FUNCTION K1(DIM,i,X1,X2,V1,V2,NDIM,ORD,nu,maxnu)RESULT (K_1);
        integer,intent(in) :: i,DIM,nu;
        real(8) :: K_1;
        real(8) :: R;
        real(8) :: B1;
        real(8),intent(in) :: X1,X2,V1,V2;
COMMON/A/M1,M2,Fgauss,H;
        integer,intent(in) :: NDIM,ORD,maxnu;
Dimension :: B1(NDIM, ORD);
Dimension :: X1(NDIM,ORD),X2(NDIM,ORD),V1(NDIM,ORD),V2(NDIM,ORD);
Dimension :: K_1(NDIM,ORD);
END FUNCTION K1;
 FUNCTION K2(DIM,i,X1,X2,V1,V2,NDIM,ORD,nu,maxnu)RESULT (K_2);
        integer,intent(in) :: i,DIM,nu;
        real(8) :: K_2;
        real(8) :: R;
        real(8) :: B2;
        real(8),intent(in) :: X1,X2,V1,V2;
COMMON/A/M1,M2,Fgauss,H;
        integer,intent(in) :: NDIM,ORD,maxnu;
Dimension :: B2(NDIM,ORD);
Dimension :: X1(NDIM,ORD),X2(NDIM,ORD),V1(NDIM,ORD),V2(NDIM,ORD);
Dimension :: K_2(NDIM,ORD);
END FUNCTION K2;
END INTERFACE;
        open(1,file='input.dat');
         open(2,file='result.res');
         open(3,file='mid.dat');
   READ(1,'(A)') STRING;
   READ(1,*)  Fgauss,H;
   READ(1,*)  M1,M2;
   READ(1,*)  X1(1,1),X1(2,1),X1(3,1),V1(1,1),V1(2,1),V1(3,1);
   READ(1,*)  X2(1,1),X2(2,1),X2(3,1),V2(1,1),V2(2,1),V2(3,1);
   WRITE(*,'(A)') STRING;
   WRITE(3,'(A)') STRING;
   WRITE(3,'(A,2G14.6)')' Fgauss,H:',Fgauss,H;
   WRITE(3,'(A,2G14.6)')' M1,M2:',M1,M2;
   WRITE(3,'(A,6G17.10)')' X1(1,1),X1(2,1),X1(3,1),V1(1,1),V1(2,1),V1(3,1):',X1(1,1),X1(2,1),X1(3,1),V1(1,1),V1(2,1),V1(3,1);
   WRITE(3,'(A,6G17.10)')' X2(1,1),X2(2,1),X2(3,1),V2(1,1),V2(2,1),V2(3,1):',X2(1,1),X2(2,1),X2(3,1),V2(1,1),V2(2,1),V2(3,1);
  R=((X1(1,1)-X2(1,1))**2.D0+(X1(2,1)-X2(2,1))**2.D0+(X1(3,1)-X2(3,1))**2.D0)**0.5D0;
        N=0;

        _WHILE N<=100 _DO;
         i=2;
          _WHILE i<=ORD _DO;
         DIM=1;

           _WHILE DIM<=NDIM _DO;
X1(DIM,i)=X1(DIM,i-1)+0.5D0*ABS(i/2)*H*K1(DIM,i-1,X1(DIM,i-1),X2(DIM,i-1),V1(DIM,i-1),V2(DIM,i-1),NDIM,ORD,2,maxnu);
X2(DIM,i)=X2(DIM,i-1)+0.5D0*H*ABS(i/2)*K2(DIM,i-1,X1(DIM,i-1),X2(DIM,i-1),V1(DIM,i-1),V2(DIM,i-1),NDIM,ORD,2,maxnu);
V1(DIM,i)=V1(DIM,i-1)+0.5D0*H*ABS(i/2)*K1(DIM,i-1,X1(DIM,i-1),X2(DIM,i-1),V1(DIM,i-1),V2(DIM,i-1),NDIM,ORD,1,maxnu);
V2(DIM,i)=V2(DIM,i-1)+0.5D0*H*ABS(i/2)*K2(DIM,i-1,X1(DIM,i-1),X2(DIM,i-1),V1(DIM,i-1),V2(DIM,i-1),NDIM,ORD,1,maxnu);

                DIM=DIM+1;
                _OD;
          i=i+1;
        _OD;

        _WHILE DIM<=NDIM _DO;
X1(DIM,1)=X1(DIM,1)+1.D0/6.D0*H*(K1(DIM,1,X1(DIM,1),X2(DIM,1),V1(DIM,1),V2(DIM,1),NDIM,ORD,2,maxnu)+2.D0*K1(DIM,2,X1(DIM,2),X2(DIM,2),V1(DIM,2),V2(DIM,2),NDIM,ORD,2,maxnu)+2.D0*K1(DIM,3,X1(DIM,3),X2(DIM,3),V1(DIM,3),V2(DIM,3),NDIM,ORD,2,maxnu)+K1(DIM,4,X1(DIM,4),X2(DIM,4),V1(DIM,4),V2(DIM,4),NDIM,ORD,2,maxnu));

X2(DIM,1)=X2(DIM,1)+1.D0/6.D0*H*(K2(DIM,1,X1(DIM,1),X2(DIM,1),V1(DIM,1),V2(DIM,1),NDIM,ORD,2,maxnu)+2.D0*K2(DIM,2,X1(DIM,2),X2(DIM,2),V1(DIM,2),V2(DIM,2),NDIM,ORD,2,maxnu)+2.D0*K2(DIM,3,X1(DIM,3),X2(DIM,3),V1(DIM,3),V2(DIM,3),NDIM,ORD,2,maxnu)+K2(DIM,4,X1(DIM,4),X2(DIM,4),V1(DIM,4),V2(DIM,4),NDIM,ORD,2,maxnu));

V1(DIM,1)=V1(DIM,1)+1.D0/6.D0*H*(K1(DIM,1,X1(DIM,1),X2(DIM,1),V1(DIM,1),V2(DIM,1),NDIM,ORD,1,maxnu)+2.D0*K1(DIM,2,X1(DIM,2),X2(DIM,2),V1(DIM,2),V2(DIM,2),NDIM,ORD,2,maxnu)+2.D0*K2(DIM,3,X1(DIM,3),X2(DIM,3),V1(DIM,3),V2(DIM,3),NDIM,ORD,2,maxnu)+K2(DIM,4,X1(DIM,4),X2(DIM,4),V1(DIM,4),V2(DIM,4),NDIM,ORD,2,maxnu));

V2(DIM,1)=V2(DIM,1)+1.D0/6.D0*H*(K2(DIM,1,X1(DIM,1),X2(DIM,1),V1(DIM,1),V2(DIM,1),NDIM,ORD,1,maxnu)+2.D0*K2(DIM,2,X1(DIM,2),X2(DIM,2),V1(DIM,2),V2(DIM,2),NDIM,ORD,1,maxnu)+2.D0*K2(DIM,3,X1(DIM,3),X2(DIM,3),V1(DIM,3),V2(DIM,3),NDIM,ORD,1,maxnu)+K2(DIM,4,X1(DIM,4),X2(DIM,4),V1(DIM,4),V2(DIM,4),NDIM,ORD,1,maxnu));

        _OD;
        R=((X1(1,5)-X2(1,5))**2.D0+(X1(2,5)-X2(2,5))**2.D0+(X1(3,5)-X2(3,5))**2.D0)**0.5D0;
          N=N+1;
 write(2,'(A,1i5,6g12.5)')' N,X1(1,1),X1(2,1),X1(3,1),X2(1,1),X2(2,1),X2(3,1):',N,X1(1,1),X1(2,1),X1(3,1),X2(1,1),X2(2,1),X2(1,1),X2(2,1),X2(3,1);
        _OD;

END PROGRAM RUNGEKUTT;

Please, help, it seems, I don't understand something in using functions!

Answer 1

MSB is on the right track, but I think there's enough here to figure out the problem. As noted, function K1 returns a two-dimension array. But all of the other operands in the expression are scalars (well, I don't know what H is, but it likely doesn't matter.) What ends up happening is that the expression evaluates to an array, the scalars getting expanded as needed to match up. You then end up with assigning an array to a scalar, and that's the cause of the error.

I am not familiar enough with Runge-Kutta to be able to suggest what you want instead. But it is likely that you want the function to return a scalar, not an array.

Answer 2

Are you calculating a scaler? If I understand what you are trying to do, the function returns a 2D array, but you only assign to one element of it. Why not have the function return a scaler value instead of an array?

The array message is about an inconsistency between the shapes of arrays in the expression. You haven't shown all of the declarations so we can't figure that out.

Coding style tips: 0) Is there a typo? Should it be Function K1 ? 1) Semi-colons aren't necessary on the end of each line. Fortran isn't C. 2) At least to me, your code would be more readable if you put all of the declarations pertaining to each variable on one line, instead of separate lines for type, intent and dimension. For example:

real, dimension (NDIM,ORD), intent (in) :: X1

EDIT after the edit of the question:

The machine written code is ugly.

It is clear that you need to do the calculation for all the dimensions. The question is where. The code shows the loops containing the function call rather than the function containing the loops. With this overall design it would make sense that you calculate a single element of the output array (ie, a scaler variable) and have that be the function return instead of having the function return an array. For this design, it makes little sense to return a 2D array containing only a single used element. And since your statement in the main program expects a scaler, you are getting the error message from the compiler. So redesign your function to return a scaler.

And it looks that you are calling K1 with the actual argument being single elements when arrays are expected. For example, you have X1(DIM,i-1) as a third argument when the function expects an array of size X1(NDIM,ORD) . This also a problem, as an inconsistency in actual (ie, call) and dummy arguments (ie, function). If function K1 is to do the work of selecting the appropriate array elements, you need to pass it the entire array. If the call is to select the appropriate array elements, then rewrite K1 to have scalers instead of arrays as input arguments. You need a consistent design.