| Summary: | Getting different answers for DLSODE demo code | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Byeong-Uk Kim <byeonguk.kim> |
| Component: | fortran | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED INVALID | ||
| Severity: | normal | CC: | gcc-bugs |
| Priority: | P3 | ||
| Version: | 4.2.0 | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | ||
Please send a question of this type to comp.lang.fortran or, indeed, to the gfortran list. We would be happy accept bug reports from you on Bugzilla but not general numerical analysis questions. Paul |
I tried to run DLSODE and its demo code that I got directly off from netlib. Surprisingly, I got different answers for some examples. Compiling option matters but I finally could get the idential numbers out of gfortran and g77 compared with what the demo code produced. At this point, I am not sure if the exactly same answer from gfortrn as the output of original demo code ensures its correctness. If so, can pgf90 (v. 5.2) and ifort (intel's fortran compiler) be wrong? Following are the example lines showing differences. These are specifically line 313 of the demo outputs. In the demo code (or text) says (note that I replaced original "E" with "D" in number expressions for my own convenience): 0.10000D+03 0.908D-08 1 0.992D+02 gfortran with -static -O1: 0.10000D+03 0.908D-08 1 0.992D+02 pgf90 with -pc 64 -O1 -Bstatic: 0.10000D+03 0.335D-09 1 0.251D+02 ifort without any option: 0.10000D+03 0.333D-08 1 0.225D+02 Does anyone know what the best way is to ensure minimizing numerical errors (or differences) between compilers? Or, a way to check if my compiled binary is indeed more accurate than others?