Re: 2 issues with Mathematica-data handling

• To: mathgroup at smc.vnet.net
• Subject: [mg111887] Re: 2 issues with Mathematica-data handling
• From: Bill Rowe <readnews at sbcglobal.net>
• Date: Tue, 17 Aug 2010 01:21:07 -0400 (EDT)

On 8/16/10 at 5:55 AM, deb.ban.10 at gmail.com (Debasish Banerjee)
wrote:

>2. I have data points with, say 14 significant digits, after the
>decimal. But when I import this in Mathematica, this automatically
>truncates this to about 6 or 7 digits. How do I get around this?

By default, Mathematica *displays* 6 significant digits even
when there are more than 6 significant digits. You can change
way numbers display by selecting after selecting the Preferences
menu item, then clicking on the appearance tab followed by
clicking on the numbers sub-tab. At that point, you can alter
the default display to suit yourself.

You can verify it is a display issue as follows:

In[2]:= a = 1/3.

Out[2]= 0.333333

Here, I've entered an expression using machine precision with
the default display of 6 digits

In[3]:= b = RealDigits[a]

Out[3]= {{3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3},0}

Here, I've used RealDigits to put all of the digits in a list

In[4]:= Length[First[b]]

Out[4]= 16

Showing, a has 16 digits even though only 6 are displayed by default.

Note, any number entered into Mathematica that includes a
decimal point and does not specifically define the precision to
be something other than machine precision will be represented
internally by Mathematica with machine precision.

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