# Is double precision for floating point calculation the default? Classic List Threaded 6 messages Open this post in threaded view
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## Is double precision for floating point calculation the default?

 Greetings, In a program, I need all my calculations, which are floating point decimal, to be double precision (accurate to 10E-16).  Is that the default, or must I make an explicit command for that precision, and if so, what is the command? Thanks. Tom -- Sent from: https://octave.1599824.n4.nabble.com/Octave-General-f1599825.html
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## Re: Is double precision for floating point calculation the default?

 On Saturday, 21 March 2020 03.59.34 WET ttonon wrote: > Greetings, > In a program, I need all my calculations, which are floating point decimal, > to be double precision (accurate to 10E-16). Is that the default, or must I > make an explicit command for that precision, and if so, what is the > command? Thanks. > > Tom   Yes it is the default:   As an example:   >> class(5) ans = double >> eps(1) ans = 2.2204e-16   -- José Matos
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## Re: Is double precision for floating point calculation the default?

 José Abílio Matos wrote > On Saturday, 21 March 2020 03.59.34 WET ttonon wrote: >> Greetings, >> In a program, I need all my calculations, which are floating point >> decimal, >> to be double precision (accurate to 10E-16).  Is that the default, or >> must I >> make an explicit command for that precision, and if so, what is the >> command? Thanks. >> >> Tom > > Yes it is the default: > > As an example: > >>> class(5) > ans = double >>> eps(1) > ans = 2.2204e-16 > > -- > José Matos Thanks.  It may be confusing because the answers contain only four significant places after the decimal point.  Is there a command to force the answer to display all 16 figures, as in >> pi ans =  3.1415926535897932?   Also a figure like 2.2204e-16 is accurate only to 2.e-16.  Correct?  (Just want to be sure.) Tom -- Sent from: https://octave.1599824.n4.nabble.com/Octave-General-f1599825.html
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## Re: Is double precision for floating point calculation the default?

 On Saturday, 21 March 2020 12.33.24 WET ttonon wrote: > >> pi > > ans = 3.1415926535897932?   See the help for format.   >> pi ans = 3.1416 >> format long >> pi ans = 3.141592653589793   > Also a figure like 2.2204e-16 is accurate only to 2.e-16. Correct? (Just > want to be sure.)   Nope. The value that you mention is the separation between the value represented and the next value represented by floating point representation.   >> eps ans = 2.220446049250313e-16   All those digits are significant. Simplifying we can say basically that we have ~16 digits for each floating point number (that is a simplified but mostly accurate picture).   > Tom     -- José Matos