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Arbitrary precision with power function

asked 2013-02-08 14:53:21 -0600

PlezzeR gravatar image

Hello! Sorry for my english. Why in Sage 5.6

numerical_approx((3**2.72), digits=200)

gives

19.850425152727527944307439611293375492095947265625000000000000000000000\ 000000000000000000000000000000000000000000000000000000000000000000000000\ 000000000000000000000000000000000000000000000000000000000

and

RealField(1000)(3**2.72)

gives

19.850425152727527944307439611293375492095947265625000000000000000000000\ 000000000000000000000000000000000000000000000000000000000000000000000000\ 000000000000000000000000000000000000000000000000000000000000000000000000\ 000000000000000000000000000000000000000000000000000000000000000000000000\ 0000000000000

? After digit 5 zero, zero, zero. How to get more digits in Sage?

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answered 2013-02-08 16:41:50 -0600

ppurka gravatar image

updated 2013-02-08 17:01:19 -0600

You have lost precision in the exponent. Use this instead:

sage: RealField(1000)(3**RealField(1000)(2.72))
19.8504251527275236501169613591809343996536832818298893731367232890539239539110192928936229752670609756876526611313601647375707220812753965333394338326864664393162650498858490630921586590646536288686549507904739021525557865246462265058167658909360187069317683688989045025859261795668964872237430699403

EDIT: In general, I think you need to ensure that you don't try to get higher precision after your computations. Rather, start with the higher precision from the very beginning.

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I understand. Thank you! It's work. Also example for maxima: fpprec:5000; bfloat(3.0b0 ^ 2.72b0); Example for GP/PARI: \p 1000 3^2.72

PlezzeR gravatar imagePlezzeR ( 2013-02-11 03:08:48 -0600 )edit

Is there a way to choose a default precision such that one does not need to keep typing RealField(1000)?

Mafra gravatar imageMafra ( 2017-03-28 17:21:57 -0600 )edit

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Asked: 2013-02-08 14:53:21 -0600

Seen: 371 times

Last updated: Feb 08 '13