View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0000945 | MetaPost | bug | public | 2015-08-16 17:30 | 2015-10-06 12:39 |
| Reporter | toby | Assigned To | |||
| Priority | normal | Severity | minor | Reproducibility | always |
| Status | new | Resolution | open | ||
| Product Version | 1.890 | ||||
| Summary | 0000945: New number systems: "uniformdeviate 4096" produces integers instead of reals | ||||
| Description | Using mpost recently compiled from trunk, I get odd results from "uniformdeviate" - "uniformdeviate 1" produces numbers that are all multiples of 1/4096. - "uniformdeviate 1024" produces multiples of 1/4 - "uniformdeviate 4096" produces integers - "uniformdeviate 8092" produces even integers and so on I guess that this is another artefact from the conversion from the scaled routines. Maybe we need a new uniform random number generator for each of the new number systems? | ||||
| Steps To Reproduce | show numbersystem; warningcheck := 0; for i=1 upto 4: x := uniformdeviate 4096; show x; endfor | ||||
| Additional Information | Here's some sample output from the above, with each of the number systems This is MetaPost, version 1.999 (TeX Live 2015) (kpathsea version 6.2.1) (/usr/local/texlive/2014/texmf-dist/metapost/base/mpost.mp (/usr/local/texlive/2014/texmf-dist/metapost/base/plain.mp Preloading the plain mem file, version 1.005) ) (./numbers.mp >> "scaled" >> 3197.13828 >> 2188.96832 >> 3010.09789 >> 3947.62305 ) Transcript written on numbers.log. This is MetaPost, version 1.999 (TeX Live 2015) (kpathsea version 6.2.1) (/usr/local/texlive/2014/texmf-dist/metapost/base/mpost.mp (/usr/local/texlive/2014/texmf-dist/metapost/base/plain.mp Preloading the plain mem file, version 1.005) ) (./numbers.mp >> "double" >> 917 >> 67 >> 1353 >> 814 ) Transcript written on numbers.log. This is MetaPost, version 1.999 (TeX Live 2015) (kpathsea version 6.2.1) (/usr/local/texlive/2014/texmf-dist/metapost/base/mpost.mp (/usr/local/texlive/2014/texmf-dist/metapost/base/plain.mp Preloading the plain mem file, version 1.005) ) (./numbers.mp >> "binary" >> 2678 >> 3060 >> 367 >> 2208 ) Transcript written on numbers.log. This is MetaPost, version 1.999 (TeX Live 2015) (kpathsea version 6.2.1) (/usr/local/texlive/2014/texmf-dist/metapost/base/mpost.mp (/usr/local/texlive/2014/texmf-dist/metapost/base/plain.mp Preloading the plain mem file, version 1.005) ) (./numbers.mp >> "decimal" >> 2270 >> 3804 >> 735 >> 1264 ) Transcript written on numbers.log. | ||||
| Tags | No tags attached. | ||||
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Looking at the source, code I see that we are still using the base random number generator which does indeed generate "fractions", which is why they come out as 1/4096s I guess. Is it too much work to override the whole mechanism? TAOCP 3.6 gives a suitable high-level language routine (albeit in Fortran). |
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Thank you for the report. I will look at it asap. |
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take_fraction is specialized for each numbersystem, so it should be ok. |
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yes but you are using 1/4096 as the resolution in the random number generator instead of 2^-28 as in the original because of the way you have implemented take_fraction for decimal. So the random numbers are not very random. Perhaps it would be better to re-write the random number generator *without* fractions? (But I can see that this would make a bunch more work elsewhere). |
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I think that I have to make a mp_unif_rand specific for each numbersystem. |
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http://www-cs-faculty.stanford.edu/~uno/programs/rng.c could be a good choice. |
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I have adapted rng.c for binary, decimal and double (trivial modifications). Now the uniform random generator has a modulo of 2^30 and a period of (2^30)^2-1=2^60-1. I will commit soon. |
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Revision 2069 still has the old generator. |
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Rev. 2070 has new generator. |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 2015-08-16 17:30 | toby | New Issue | |
| 2015-08-17 16:57 | toby | Note Added: 0001397 | |
| 2015-09-14 18:20 | luigi scarso | Note Added: 0001403 | |
| 2015-09-14 21:43 | luigi scarso | Note Added: 0001405 | |
| 2015-09-14 23:59 | toby | Note Added: 0001406 | |
| 2015-09-16 00:40 | luigi scarso | Note Added: 0001407 | |
| 2015-09-18 10:29 | luigi scarso | Note Added: 0001408 | |
| 2015-09-22 11:50 | luigi scarso | Note Added: 0001410 | |
| 2015-09-23 12:40 | luigi scarso | Note Added: 0001411 | |
| 2015-10-06 12:39 | luigi scarso | Note Added: 0001413 |
