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POFortran subroutine fails on return
 

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  1. POFortran subroutine fails on return
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    <p>I have a Fortran numerical code that calls a subroutine from an external module. This code has been running fine for me until I tried to compile and run on a different machine. On the new machine, my program crashes fairly quickly.</p> <p>Using debug print statements, I have isolated that the crash occurs on return from the external subroutine. The main program calls the subroutine several times, and the crash occurs on return from the second call to the subroutine (the first call works fine). It always crashes on the second subroutine call with this set of input data, but with another set of input data (roughly 1/3 the size of the first), it crashes on return from the fifth subroutine call.</p> <p>The symptoms suggest to me that something is getting stored in memory each time and accumulates over each subroutine call until it runs out of space, but I'm not sure what that is or how that would occur. The code is hard to simplify to a minimal working example, but I have posted the relevant portion below. Let me know if there is something else that would be helpful to see. It is basically fixed form Fortran 90.</p> <pre><code> use fd implicit none integer, parameter :: ms = 2000 integer n real(dp), dimension(ms) :: s real(dp), dimension(ms) :: e real(dp), dimension(ms) :: f real(dp), dimension(ms) :: d1f real(dp), dimension(ms) :: d2f real(dp), dimension(ms) :: c, d real(dp), dimension(ms) :: a real(dp), dimension(ms) :: b real(dp), dimension(ms) :: temp integer w integer k real(dp) th do i = 1,n temp(i) = a(i) end do call lprsmf(s(1:n),temp(1:n),n,w,k,th,a(1:n),d1f(1:n), * d2f(1:n)) do i = 1,n temp(i) = b(i) end do call lprsmf(s(1:n),temp(1:n),n,w,k,th,b(1:n),d1f(1:n), * d2f(1:n)) do i = 1,n temp(i) = c(i) end do call lprsmf(s(1:n),temp(1:n),n,w,k,th,c(1:n),d1f(1:n), * d2f(1:n)) do i = 1,n temp(i) = d(i) end do call lprsmf(s(1:n),temp(1:n),n,w,k,th,d(1:n),d1f(1:n), * d2f(1:n)) do i = 1,n temp(i) = e(i) end do call lprsmf(s(1:n),temp(1:n),n,w,k,th,e(1:n),d1f(1:n), * d2f(1:n)) do i = 1,n temp(i) = f(i) end do call lprsmf(s(1:n),temp(1:n),n,w,k,th,f(1:n),d1f(1:n), * d2f(1:n)) </code></pre> <p>module <code>fd</code>:</p> <pre><code> module fd ! Double precision real kind integer, parameter :: dp = selected_real_kind(15) contains subroutine lprsmf(x,y,n,w,k,th,s,d1,d2) ! INPUTS: ! x, y, n, w, k, th ! OUTPUTS: ! s, d1, d2 implicit none real(dp), dimension(n) :: x,y,s,d1,d2 integer n,w,k real(dp) th ! ... code here ... end subroutine lprsmf end module fd </code></pre> <p>My compiler is gfortran 4.6.1. Besides getting the code to stop crashing, I really would like to understand what is fundamentally going on with the argument passing (as I assume the problem lies with the array slices being passed out of the program). Note that <code>a,b,c,d,e,f,s,temp,d1f,d2f</code> have length 2000, while <code>n</code>, which represents the range of valid data, is in the range 100-500, depending on the input data length.</p> <p><strong>EDIT:</strong> The error message is Windows putting up a dialog informing me that the program has stopped working.</p>
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    1. COMy first thought is to be absolutely certain that the reals you are passing to the routine are indeed double precision, as the routine calls for. More precisely, make sure of what byte size the routine wants to see in its dp arguments (probably 8, _but not necessarily_) and make sure that is the same as the byte size of the real arguments being passed. Different compilers handle the precision of real numbers differently.
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      1. USbob.sacamento
    2. CO@bob.sacamento, I'm pretty sure they're the same, but is there an intrinsic function to check byte size?
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    3. COWhen I want this kind of info, I usually read the compiler documentation, but you can get this info from the "KIND" Fortran intrinsic. If "r" is a real*8, kind(r) will return 8. Alternatively, you can be double sure by editing the code so that the size of reals are absolutely specified, i.e. instead of "real", declare with "real(kind=4)" and instead of "double precision", declare with "real(kind=8)".
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