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Beginner
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Error when use variables in Fortran module

I am encountering a very very strange error when I use variables in Fortran module with intel/18.0.2.

It's a quite simple code. Each column of 'F' is calculated by each column of 'X'. They are both variables in module global. Below is the code.

In global.f90: declaration of the module.

module global
implicit none
!  Parameters
real(8),parameter :: GravConst = 6.674184D-11
real(8),parameter :: PI = 3.141592653589793D0
integer :: N
real(8) :: X(3,2)
real(8) :: F(3,2)
real(8) :: omega
real(8) :: density
end module

In main.f90: calculation of 'F'.

program main
use global
implicit none

integer I,J,K
N = 2
F = 0.0D0
X = 0.0D0
omega = 1.0
density = 0.0

!  read positions
open (1,FILE="pos.txt")
do I = 1,N
    read(1,*) (X(K,I),K=1,3)
end do

write(*,*) 'X:',(X(J,2),J=1,3)
write(*,*) 'F:',(F(J,2),J=1,3)
write(*,*) 'F(1,2):',omega*omega*X(1,2)- 4.0D0/3.0D0*PI*GravConst*density*X(1,2)
write(*,*) 'F(2,2):',omega*omega*X(2,2)- 4.0D0/3.0D0*PI*GravConst*density*X(2,2)
do I = 1,N
    !yorp force
    do K = 1,2
        F(K,I) = F(K,I) + omega*omega*X(K,I)
    end do  
    !gravity      
    do K = 1,3
        F(K,I) = F(K,I) - 4.0D0/3.0D0*PI*GravConst*density*X(K,I)
    end do
end do
write(*,*) (F(J,2),J=1,3)
end

F(1,2) and F(2,2) calculated directly are printed before the loop. Note that omega=1, and density=0, so F(1,2) and F(2,2) should equal to X(1,2) and X(2,2), respectively. After the loop, the final values of F(:,2) are printed. Here is the result using intel/18.0.2. It's obvious that the result calculated by the loop is wrong.

X: -4.97716000000000       0.897938000000000       -11.4228000000000
F: 0.000000000000000E+000  0.000000000000000E+000  0.000000000000000E+000
F(1,2): -4.97716000000000
F(2,2): 0.897938000000000
-4.69400000000000       -4.97716000000000    0.000000000000000E+000

It seem like something strange happening in the loop... But if I change the order of the calculation in the loop, the result would be correct.

do I = 1,N 
    !gravity      
    do K = 1,3
        F(K,I) = F(K,I) - 4.0D0/3.0D0*PI*GravConst*density*X(K,I)
    end do
    !yorp force
    do K = 1,2
        F(K,I) = F(K,I) + omega*omega*X(K,I)
    end do 
end do

X: -4.97716000000000       0.897938000000000       -11.4228000000000
F: 0.000000000000000E+000  0.000000000000000E+000  0.000000000000000E+000
F(1,2): -4.97716000000000
F(2,2): 0.897938000000000
-4.97716000000000       0.897938000000000    0.000000000000000E+000

If I use local variables rather variables in module, or use intel/15.0.6, the result would also be correct.

 

Below are pos.txt and makefile I used.

2.64530000  -7.20517000     -4.69400000 
-4.97716000     0.89793800  -11.42280000

# Start of the makefile
COMPILER=ifort -O2
DEMBody: global.o main.o
    $(COMPILER)  -o DEMBody global.o main.o
global.mod: global.o global.f90
    $(COMPILER)  -c global.f90
global.o: global.f90
    $(COMPILER)  -c global.f90
main.o: global.mod main.f90
    $(COMPILER)  -c main.f90
clean:
    rm global.mod global.o main.o
# End of the makefile

 

Or, you could try this input. It would be more clear.

    X(1,1) = 1.0
    X(2,1) = 2.0
    X(3,1) = 3.0
    X(1,2) = 4.0
    X(2,2) = 5.0
    X(3,2) = 6.0

You would get a confusing result for 'F':

    F(:,1): 1.000        2.000       0.000E+000
    F(:,2): 3.000        4.000       0.000E+000

The correct result should be

    F(:,1): 1.000        2.000       0.000E+000
    F(:,2): 4.000        5.000       0.000E+000

It seems that the element of X/F has been moved by one cell.

 

 

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3 Replies
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New Contributor II
24 Views

This is indeed strange.  My old compiler (11.075) gives the correct results.

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Highlighted
Black Belt
24 Views

This appears to be an optimizer bug. Compiling with the /Od option leads to correct behavior.

Please report the bug to https://supporttickets.intel.com/servicecenter?lang=en-US .

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Highlighted
Beginner
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Yes, I tried '-fp-model strict' and got correct result. It seems that compilers after intel/17.0.7 has this bug. 

mecej4 wrote:

This appears to be an optimizer bug. Compiling with the /Od option leads to correct behavior.

Please report the bug to https://supporttickets.intel.com/servicecenter?lang=en-US .

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