IMSL IVPAG: Differences in Release and Debug mode

[jossl]

Hi, I am solving a set of very stiff PDEs with the DIVPAG solver of the IMSL 6.0 libraries. For some set of initial/boundary conditions error 7 is returned (see below) when the simulation is run in release mode, but the exact same simulation runs well in debug mode. I have already increased my tolerance as much as possible. Does any one know what the issue could be? Thanks PS. I know an example of the code could be helpful but the code is long and complex, and it is not possible to have a minimal example... Output in release mode: ------------------------------------------------------------------------------------------------------ *** FATAL ERROR 7 from DIVPAG. Integration halted after failing to *** achieve corrector convergence, even after reducing the stepsize *** by a factor of 1.0E+10 to H = 1.000000000000001D-13. TOL = *** 1.000000000000000D-07 may be too small. Press any key to continue . . .

[Steven_L_Intel1]

Enabling optimizations can mean small differences in values depending on order of operations, vectorization, etc. You may have uninitialized variables. The first thing I would do is add diagnostic output before the call to IVPAG with the hex representation of all of the input values - do this in the debug and release versions and see where they differ, if they do. You may also be passing wrong sizes to DIVPAG (that you are using that name tells me you are using the Fortran 77 interface - have you tried switching to the "Fortran 90" interface with USE IVPAG_INT and calling IVPAG (check the documentation for the argument list)?