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When I use a array in a function with fortran,if i use teo array at a statement,sometimes it doesn't.
function f integer,intent(in)::n real(rkind)::f(n,n) real(rkind),intent(in)::a(n,n) integer::i,j real(rkind)::b(n,n),c(n),d do j=2,n do i=1,j-1 d=b(i,j)/b(j,j) b(i,:)=b(i,:)-d*b(j,:) f(i,:)=f(i,:)-d*f(j,:) !This code Works properly end do end do do j=2,n do i=1,j-1 b(i,:)=b(i,:)-b(i,j)/b(j,j)*b(j,:) f(i,:)=f(i,:)-d*f(j,:) !This code doesn't work end do end do end function f
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In your code, the value of b(I,j)/b(j,j) is not the same on line 47 as on line 46 because you change b(I,j) on line 46.
You're using d on lines 20 and 21, which is the same on both lines.
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Can we assume the arrays b and f are local variables?
You dont show any initialization for b or f so they could have any value.
Exactly what do you mean by it working or not working?
Please supply a self contained example we could compile.
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This is the code,in this code,variable 'b' and 'c' should have the same value,but it dosen't.And the correct one should be 'b'. Function 'f1' and 'f2' just have one statement which is different,and I have note that place.The different statement should have same effect,but they are not now.(my English is poor,If I have some wrong in my reply ,plseae forgive me)
module test contains function f1(a,n) integer,intent(in)::n real(16)::f1(n,n) real(16),intent(in)::a(n,n) integer::i,j,m real(16)::b(n,n),c(n),d b=a f1=0 do i=1,n f1(i,i)=1 end do do j=1,n do i=j+1,n d=b(i,j)/b(j,j) b(i,j:)=b(i,j:)-d*b(j,j:) !different place f1(i,:)=f1(i,:)-d*f1(j,:) end do end do end function f1 function f2(a,n) integer,intent(in)::n real(16)::f2(n,n) real(16),intent(in)::a(n,n) integer::i,j,m real(16)::b(n,n),c(n),d b=a f2=0 do i=1,n f2(i,i)=1 end do do j=1,n do i=j+1,n b(i,j:)=b(i,j:)-b(i,j)/b(j,j)*b(j,j:) !different place,and just replace 'd'with'b(i,j)/b(j,j)' f2(i,:)=f2(i,:)-b(i,j)/b(j,j)*f2(j,:) end do end do end function f2 end module test program main use test implicit none integer,parameter::n=3 real(16)::x(n),y(n),a(n,n),b(n,n),c(n,n) a=reshape([2,4,-2,1,1,2,1,0,1],[3,3]) b=f1(a,n) c=f2(a,n) write(*,*)b write(*,*) write(*,*) write(*,*) write(*,*) write(*,*) write(*,*)c read(*,*) end program main
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I ran your example and B /= C. A changed the function f1 and f2 to subroutines. The results are exactly the same.
I changed real(16) to real(8). The results are the same.
I think the logic of calculation in the loops is incorrect. I don't think this is a compiler problem.
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In your code, the value of b(I,j)/b(j,j) is not the same on line 47 as on line 46 because you change b(I,j) on line 46.
You're using d on lines 20 and 21, which is the same on both lines.
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