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Jeff
Posts:
113
Registered:
11/22/09


Re: How to import data without losing much precision
Posted:
Dec 3, 2012 4:44 PM


Hi Steven. Thanks for your reply.
"Steven_Lord" <slord@mathworks.com> wrote in message <k9h7q6$4sk$1@newscl01ah.mathworks.com>... > > > "Jeff " <spREMOVEHITSjeffAT@SIGNoptonline.net> wrote in message > news:k9gk4s$2hh$1@newscl01ah.mathworks.com... > > I'm trying to import some data, which was created by C code, into Matlab > > without losing much precision. Can someone show me an example of how to do > > so? > > > > I have about 52 decimal places of precision, with N=16 numbers on a line, > > like this: > > Double precision only allows you 52 bits of precision (well, plus the > implicitly stored bit) not 52 digits.
The input data is 52 decimal digits, not bits, of precision. I know what I posted was a big mess (there's no preview on this board), but there are 52 decimal digits of precision in the sample input. It's a "long double" in C. If my Matlab has only 52 (or 53) binary digits of precision, which is 16 decimal digits, then I guess I've already imported the most precise information I can.
> > *snip* > > > I've tried using dlmread, csvread and importdata, but they cut off > > precision. > > You could read these in as _strings_ and convert them into symbolic objects > using Symbolic Math Toolbox. > > *snip* > > > I've tried other things, too, but I cannot get any more precision. You can > > see that their all losing precision after about 16 decimal places. > > Yes. See: > > http://en.wikipedia.org/wiki/Doubleprecision_floatingpoint_format > > > Could someone show me an example of how to import my data with the most > > precision? > > Why do you believe you need 52 decimal digits of precision for your data? > For comparison, you only need roughly 39 digits of pi to calculate the > volume of the universe to within one atom. > > http://en.wikipedia.org/wiki/Pi#Motivations_for_computing_.CF.80 > > Just because you HAVE the number out to N digits doesn't mean you NEED all > those digits.
Actually, I don't know how much precision I should preserve. My adviser has been characteristically slow to respond to my questions and I've learned that I need to keep working while waiting for his response. If I don't need that much precision, then hopefully I will have at least learned something valuable along the way.
Maybe my real question should have been "How do I determine how much precision my version of Matlab has?"
> >  > Steve Lord > slord@mathworks.com > To contact Technical Support use the Contact Us link on > http://www.mathworks.com



