FORTRAN-Invalid write of size 4 - fortran

Question

I have written a Fortran code using MPI, as I am new to valgrind I could not manage to find the problem. I get this error while running the check:
==3040== Invalid write of size 4
==3040== at 0x804BFE0: MAIN__ (NS.f90:174)
==3040== by 0x804E190: main (NS.f90:321)
==3040== Address 0x5746f20 is 0 bytes after a block of size 8 alloc'd
==3040== at 0x402BE68: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==3040== by 0x804C5F3: MAIN__ (NS.f90:198)
==3040== by 0x804E190: main (NS.f90:321)
==3040==
==3041== Invalid write of size 4
==3041== at 0x804BFE0: MAIN__ (NS.f90:174)
==3040== Invalid write of size 4
==3040== at 0x804C036: MAIN__ (NS.f90:175)
==3040== by 0x804E190: main (NS.f90:321)
==3041== by 0x804E190: main (NS.f90:321)
==3041== Address 0x5748bbc is 0 bytes after a block of size 12 alloc'd
==3041== at 0x402BE68: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==3040== Address 0x5746f58 is 0 bytes after a block of size 8 alloc'd
==3040== at 0x402BE68: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==3040== by 0x804C729: MAIN__ (NS.f90:198)
==3040== by 0x804E190: main (NS.f90:321)
==3040==
==3041== by 0x804C5F3: MAIN__ (NS.f90:198)
==3041== by 0x804E190: main (NS.f90:321)
==3041==
==3040== Invalid write of size 4
==3040== at 0x804C087: MAIN__ (NS.f90:176)
==3040== by 0x804E190: main (NS.f90:321)
==3040== Address 0x5746f90 is 0 bytes after a block of size 8 alloc'd
==3040== at 0x402BE68: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==3040== by 0x804C862: MAIN__ (NS.f90:198)
==3040== by 0x804E190: main (NS.f90:321)
==3040==
==3041== Invalid write of size 4
==3041== at 0x804C036: MAIN__ (NS.f90:175)
==3041== by 0x804E190: main (NS.f90:321)
==3041== Address 0x5748bfc is 0 bytes after a block of size 12 alloc'd
==3041== at 0x402BE68: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==3041== by 0x804C729: MAIN__ (NS.f90:198)
==3041== by 0x804E190: main (NS.f90:321)
==3041==
==3040== Invalid write of size 4
==3040== at 0x804C1C5: MAIN__ (NS.f90:178)
==3040== by 0x804E190: main (NS.f90:321)
==3040== Address 0x5746fc8 is 0 bytes after a block of size 8 alloc'd
==3040== at 0x402BE68: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==3040== by 0x804C99B: MAIN__ (NS.f90:198)
==3040== by 0x804E190: main (NS.f90:321)
==3040==
==3041== Invalid write of size 4
==3041== at 0x804C087: MAIN__ (NS.f90:176)
==3041== by 0x804E190: main (NS.f90:321)
==3041== Address 0x5748c3c is 0 bytes after a block of size 12 alloc'd
==3041== at 0x402BE68: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==3041== by 0x804C862: MAIN__ (NS.f90:198)
==3041== by 0x804E190: main (NS.f90:321)
==3041==
==3040==
==3041== Invalid write of size 4
==3041== at 0x804C1C5: MAIN__ (NS.f90:178)
==3041== by 0x804E190: main (NS.f90:321)
==3041== Address 0x5748c7c is 0 bytes after a block of size 12 alloc'd
==3041== at 0x402BE68: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
Line 174 to 178 contains this piece of code:
A(I) = -0.5 * (0.5 * (1.0 + EPX) * CX(I-1, J) + DX)
B(I) = (1 + DX + 0.5 * EPX * CX(I, J))
C(I) = 0.5 * (0.5 * (1 - EPX) * CX(I+1, J) - DX)
R(I) = 0.5 * (0.5 * (1 + EPY) * CY(I, J-1) + DY) * OMEGA(I, J-1) + (1 - DY - 0.5 * EPY * CY(I, J)) * OMEGA(I, J) + 0.5 * (-0.5 * (1 - EPY) * CY(I, J+1) + DY) * OMEGA(I, J+1)
Can anybody tell me what is wrong here? I am also getting other errors like:
==3041== Invalid read of size 4
==3041== at 0x804C271: MAIN__ (NS.f90:183)
==3041== by 0x804E190: main (NS.f90:321)
==3041== Address 0x5748c40 is 4 bytes after a block of size 12 alloc'd
==3041== at 0x402BE68: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
where line 183 referring to:
R(N) = R(N) - C(N) * OMEGA(N+1, J)
I would appreciate if someone can tell me where the problem lies.
Here is the block of code:
A = 0.0
B = 0.0
C = 0.0
R = 0.0
X = 0.0
DO J = 1, M
DO I = 1, N
IF (U(I, J) > 0.0) THEN
EPX = 1.0
ELSE
EPX = -1.0
ENDIF
IF (V(I, J) > 0.0) THEN
EPY = 1.0
ELSE
EPY = -1.0
ENDIF
A(I) = -0.5 * (0.5 * (1.0 + EPX) * CX(I-1, J) + DX)
B(I) = (1 + DX + 0.5 * EPX * CX(I, J))
C(I) = 0.5 * (0.5 * (1 - EPX) * CX(I+1, J) - DX)
R(I) = 0.5 * (0.5 * (1 + EPY) * CY(I, J-1) + DY) * OMEGA(I, J-1) + (1 - DY - 0.5 * EPY * CY(I, J)) * OMEGA(I, J) + 0.5 * (-0.5 * (1 - EPY) * CY(I, J+1) + DY) * OMEGA(I, J+1)
ENDDO
R(1) = R(1) - A(1) * OMEGA(0, J)
R(N) = R(N) - C(N) * OMEGA(N+1, J)
ENDDO

Answer 1

It is very probable you are getting index errors and you overflow the array boundaries. This is a common mistake and the compilers can assist in debugging. For gfortran use -fcheck=all, for Intel us -check all. Other compilers also have similar capabilities.
After that, you have to make sure your arrays have proper dimensions and you are running the loops with proper upper and lower values.
We cannot say where the error is in this case, because you do not show the declarations of your variables.