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MathGroup Archive 2000

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Re: Re: PrintPrecision

  • To: mathgroup at smc.vnet.net
  • Subject: [mg23175] Re: [mg23160] Re: PrintPrecision
  • From: David Withoff <withoff at wolfram.com>
  • Date: Thu, 20 Apr 2000 23:48:46 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

> In article <8djlqq$7rj at smc.vnet.net>, "John Flint" <j.flint at itf.sdu.dk> wrote:
> 
> :When I use the Options Inspector to change the notebook 'Formatting
> :Options', 'Expression Formating', 'Display Options', 'PrintPrecision' to say
> :3 in order to see more of a matrix in my window then som numbers come
> :out as expected (ex. -3.22) while others still have a lot of digits (ex.
> :27.536488564494144). How can I make them all small?
> 
> I'm sick to death of the bizarre formatting rules which Mathematica 
> uses.  I want a plain, simple, fixed-format, in which a "1" will print 
> as a "1.0000" (NOT "1.") and a "1.39281" will print as a "1.3928" and a 
> "1.31" will print as a "1.3100".  I've tried NumberForm, I've tried 
> PaddedForm, I've tried writing the damned things to a file--and I cannot 
> get the simple, classical, traditional "f6.4".  HOW DO I DO THIS?!
> 
> And when I print it to a file, I **don't** want to find the file filled 
> with a bunch of "NumberForm[..."'s.
> 
> And as I mentioned in another post, **my** Options Inspector won't make 
> any changes.
> 
> --Ron Bruck

PaddedForm[expr, {6, 4}] did what you described when I tried it.

In[1]:= PaddedForm[1, {6, 4}]

Out[1]//PaddedForm=   1.0000

In[2]:= PaddedForm[1.39281, {6, 4}]

Out[2]//PaddedForm=   1.3928

In[3]:= PaddedForm[1.31, {6, 4}]

Out[3]//PaddedForm=   1.3100

PaddedForm also works for writing this format to a file.

In[4]:= Write["file", OutputForm[PaddedForm[
            ColumnForm[{1, 1.39281, 1.31}], {6, 4}]]]

In[5]:= Close["file"] ;

In[6]:= !!file
  1.0000
  1.3928
  1.3100

The Option Inspector is irrelevant for this task.  The PrintPrecision option
controls the number of digits used to display machine inexact numbers in
typeset formats (StandardForm and TraditionalForm).  This will have no
effect on the display of the integer 1, or on the display of high-precision
numbers, or in non-typeset formats such as OutputForm that are typically
of interest when writing numbers to a file.

It would not be terribly difficult to program formatting functions in
Mathematica to replicate Fortran-like syntax for format control, so
you could for example enter MyForm[1.39281, f6.4] and get essentially
what you get in Fortran. The functionality Mathematica is sufficiently
similar to the functionality of Fortran for these kinds of tasks that I
don't see a good reason (other than not wanting to learn new notation)
to prefer one over the other, but perhaps someone who sees a good
reason to do so will program this aspect of Fortran syntax into
Mathematica some day.

It is unlikely that your Option Inspector won't make any changes, but
hopefully someone else will address that issue.

Dave Withoff
Wolfram Research


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