03 DSD-NL 2016 - Simona Gebruikersmiddag - Floating point onnauwkeurigheid en gevoeligheid van rekenmodellen - Edwin Spee, Deltares

1. 20 juni 2016
Sensitivity within Waqua models
Edwin Spee, Deltares

2. Background
• Helpdesk-issue: differences in RMM due to location of RGF-file
• Testbank tools: differences in array opdist
• Never heard of opdist …
• LDS : “It gives for each opening point the distance of the point to
the start of the opening to which it belongs.”
• gives a hint: it uses differences between grid coordinates:
d = 4.435234E+05 - 4.436052+05 = -81.8
• first guess: may be related to compiler options
20 juni 2016

3. Location boundary points
20 juni 2016
43.576

4. 20 juni 2016

5. Array opdist itself
20 juni 2016

6. Difference due to location RGF file
20 juni 2016

7. Simona2016: difference due to RGF file
20 juni 2016
Calculation of opdist now in double precision

8. Difference Simona2015 – Simona2016
20 juni 2016

9. Effect Fp_model on cpu time
Maas (4 cores) Kuststrook (1 core)
reference 239.4 639.7
Fp_model = strict 240.5 ( + 0.5 %) 646.2 ( + 1 %)
20 juni 2016
results for double precision;
single precision still to be done.

10. discussion
• unexpected differences found in RMM model
• presentation Werner Kramer: explained by alignment data
• hard to get data aligned within Simona (ibuffr 32 bit ; exe 64 bit)
• problem with RMM fixed by using double precision in part of
Waqpre.
• more code in double precision, gives differences between
Simona2015 and Simona2016.
20 juni 2016