Maybe a very naive question, but when I code something like:
RDD=RealBallField(256)
RDD(3.1)*RDD(2.1)
I obtain:
[6.510000000000000461852778244065128704839826135899304117285652827862296732064351 +/- 9.03e-80]
as the output. Where does all the noise after the 15th digit come from and how could I get rid of it?
Or am I not allowed to increase the accuracy above 53 when using ARB in SageMath?
Note that number 3.1 has precision of 53 bits as an element of RDF and this precision is inherited by RDD object. Try this instead:
RDD("3.1")*RDD("2.1")
Alternative :
sage: RDD(QQ(3.1))*RDD(QQ(2.1))
[6.510000000000000000000000000000000000000000000000000000000000000000000000000 +/- 3.82e-76]
HTH,
This is not an answer, but a possible clue that it is a problem of ARB and not the SageMath wrapper.
When I run this code in my IDE:
#include "flint/arb.h"
int main(int argc, char **argv)
{
arb_t a;
arb_init(a);
slong prec;
prec = 256;
arb_set_d(a, 1.1);
arb_printd(a, 40);
printf(" WRONG \n");
arb_set_str(a, "1.1", prec);
arb_printd(a, 40);
printf(" FINE \n");
arb_set_d(a, 1);
arb_printd(a, 40);
printf(" FINE \n");
arb_clear(a);
return 0;
}
I obtain:
1.100000000000000088817841970012523233891 +/- 0 WRONG
1.100000000000000000000000000000000000000 +/- 1.7272e-77 FINE
1.000000000000000000000000000000000000000 +/- 0 FINE
This clearly shows that the issue originates from the "arb_det_d" function when fed with a non-integer value. I will ask about this on the FLINT GitHub issue list.
EDIT: Here is the ARB/Flint thread adequately explaining the observed phenomenon and showing my lack of understanding of what "inexactness" implies: https://github.com/flintlib/flint/iss...
Asked: 2024-02-18 18:27:56 +0100
Seen: 229 times
Last updated: Feb 18
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