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In the relativistic correction, the term del = sqrt(1+x) - 1 is used with a rather small value of x (often 1e-8 or such). This gives inaccurate results because of the subtraction of 1 from a number very close to 1. To improve this, the right term is extended by sqrt(1+x)+1, which gives del = x / (sqrt(1+x) + 1) without a subtraction of two equally large numbers and therefore a better accuracy. This helps on i386 FPU. The test is adjusted as well.
Contributor
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@scottransom can you take a look at this with regard to whether this patch is suitable for upstream SOFA? See also #33. |
Member
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@scottransom - just to check, did you also pass this along to the sofa board when discussing #40 ? |
Member
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@scottransom just mentioned in #40 that this is a good fix, so I'll just go ahead and merge this. Probably we can just remove it again at the next SOFA release, but just in case... Thanks @olebole! |
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In the relativistic correction, the term
is used with a rather small value of
x(often 1e-8 or such). This gives inaccurate results because of the subtraction of 1 from a number very close to 1.To improve this, the right term is extended by
sqrt(1+x)+1, which giveswithout a subtraction of two equally large numbers and therefore a better accuracy. This helps
on i386 FPU.to get on all platform results that are as excellent as with the x87 FPU ;-)The test is adjusted as well.
This will fix #33.