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## Re: Is double precision for floating point calculation the default?

 From: Benson Muite Subject: Re: Is double precision for floating point calculation the default? Date: Sat, 21 Mar 2020 15:54:31 +0300 User-agent: Cyrus-JMAP/3.1.7-1021-g152deaf-fmstable-20200319v1

```On Sat, Mar 21, 2020, at 3:33 PM, ttonon wrote:
> 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
>
To display all 16 digits use type
>>format long
>>pi
Not quite, floating point number are represented by a mantissa and an exponent.
Mantissa can have 16 digits in double precision. Some information on floating
point is at:
https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html
https://ryanstutorials.net/binary-tutorial/binary-floating-point.php
https://en.wikipedia.org/wiki/Floating-point_arithmetic
https://en.wikipedia.org/wiki/IEEE_754
>

```