error forrtl: severe (174): SIGSEGV, segmentation fault occurred matrix multiplication - fortran

Question

I tried to implement an easy Matrix multiplication, but I Keep getting the error
forrtl: severe (174): SIGSEGV, segmentation fault occurred
Image PC Routine Line Source
test_performance. 00000000004708F1 Unknown Unknown Unknown
test_performance. 000000000046F047 Unknown Unknown Unknown
test_performance. 000000000043F544 Unknown Unknown Unknown
test_performance. 000000000043F356 Unknown Unknown Unknown
test_performance. 0000000000423DFF Unknown Unknown Unknown
test_performance. 000000000040384D Unknown Unknown Unknown
libpthread.so.0 00002AD8B44769F0 Unknown Unknown Unknown
test_performance. 00000000004034A8 Unknown Unknown Unknown
test_performance. 0000000000402ECE Unknown Unknown Unknown
libc.so.6 00002AD8B46A6BE5 Unknown Unknown Unknown
test_performance. 0000000000402DD9 Unknown Unknown Unknown
This is my Code:
PROGRAM test_performance
IMPLICIT NONE
INTEGER :: DIM_M, DIM_L, DIM_N, index1, index2,index3,index4
INTEGER, DIMENSION(4,4) :: A,B,C
DIM_L=4
DIM_M=4
DIM_N=4
DO index1=1,DIM_M
DO index2=1,DIM_L
print *, 'here I am!'
A(index1,index2)=index1+index2
END DO
END DO
DO index3=1,DIM_L
DO index4=1,DIM_N
B(index3,index4)=index3+index4
END DO
END DO
print *,'A= ',A
print *,'B= ',B
CALL MATRIXMULTIPLICATION
PRINT *, 'C=', C
END PROGRAM test_performance
SUBROUTINE MATRIXMULTIPLICATION(A,B,C, DIM_M, DIM_L, DIM_N)
INTEGER, INTENT(IN) :: DIM_M, DIM_L, DIM_N
INTEGER, INTENT(IN) :: A(4,4), B(4,4)
INTEGER, INTENT(OUT) :: C(4,4)
INTEGER :: ii=1,jj=1, kk=1
DO ii=1, DIM_M
DO jj=1, DIM_N
DO kk=1, DIM_L
C(ii,jj)=C(ii,jj)+A(ii,ll)*B(ll,jj)
END DO
END DO
END DO
END SUBROUTINE MATRIXMULTIPLICATION
I don't know why I get this error, since the Dimension and all the Indices should just be fine. I tried to find the error by using all possible stuff, but I don't havy any clue anymore what the error could be.

Answer 1

The statement
CALL MATRIXMULTIPLICATION
doesn't include the arguments needed when the routine is called. A poor solution would be to simply replace that statement by
CALL MATRIXMULTIPLICATION(A,B,C, DIM_M, DIM_L, DIM_N)
A better solution would be, however, to make the subroutine's interface explicit. There are a number of ways of doing this, one by putting it into a module and useing the module. For a single subroutine that might be overkill but is definitely the way to go as your programs become larger and more complex.
A simple straightforward and satisfactory for your current purposes solution would be to move the line
END PROGRAM test_performance
to follow the line
END SUBROUTINE MATRIXMULTIPLICATION
and, where the end program line originally was insert the line
contains
If you had written your program along these lines in the first place the compiler would have seen your egregious error and pointed it out to you. As it stands the subroutine is external to the program and the compiler can't match its dummy and actual arguments at compile time; as written that argument matching is the programmer's responsibility, one you've rather fluffed.
Further improvements would be to make your subroutine handle arrays of any size and to not bother passing the array dimensions through the argument list. Fortran arrays carry their size and shape information with them, on the rare occasion a routine needs to know them explicitly it can make enquiries.
Even easier would be to use the matmul intrinsic and to spend your time programming other, perhaps more challenging and more interesting, parts of your code.