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From: James Stein on 26 May 2010 07:09
Evaluating:

ToExpression [ ToString [ 1/3 ] ]

I did not expect negative three!

Bug? or a lack in my understanding?


From: Sunt on 27 May 2010 06:42
On May 26, 7:09 pm, James Stein <mathgr...(a)stein.org> wrote:
> Evaluating:
>
> ToExpression [ ToString [ 1/3 ] ]
>
> I did not expect negative three!
>
> Bug? or a lack in my understanding?

Hi,
ToString gives an ouputform as default.
So this would be OK--
ToExpression[ToString[1/3, InputForm]]

From: Bob Hanlon on 27 May 2010 06:44

You don't want OutputForm as the input to ToString

ToString[1/3] // FullForm

"1\n-\n3"

ToExpression[ToString[#[1/3]]] & /@
{InputForm, StandardForm,
TraditionalForm, OutputForm}

{1/3, 1/3, 1/3, -3}


Bob Hanlon

---- James Stein <mathgroup(a)stein.org> wrote:

=============
Evaluating:

ToExpression [ ToString [ 1/3 ] ]

I did not expect negative three!

Bug? or a lack in my understanding?



From: gekko on 27 May 2010 06:44
On May 26, 9:09 pm, James Stein <mathgr...(a)stein.org> wrote:
> Evaluating:
>
> ToExpression [ ToString [ 1/3 ] ]
>
> I did not expect negative three!
>
> Bug? or a lack in my understanding?

This is quite an amusing behaviour, but I probably wouldn't call it a
bug. If you look at the output of the ToString call you'll see it
converts the fraction into:

1
-
3

which is the old-style way of displaying fractions on multiple lines.
Unfortunately, when you convert back to input using ToExpression,
Mathematica interprets this as several lines of input: "1" followed by
"-3" (note the "-" operator acts across lines, so the 2nd and 3rd line
are treated as a single line of input).

To get around this, you can tell ToString what form of output to use.
E.g. this does what you want:

In[285]:= ToString[1/3, InputForm]
Out[285]= 1/3
In[286]:= ToExpression[%]
Out[286]= 1/3

Cheers, P.

From: dh on 27 May 2010 06:44
Hi James,
TosTring[1/3] creates a 2 dimensional output form for this expression:
ToString[1/3] // FullForm
Obviously Mathematica can no more correctly interpret this form. I
consider this a bug you should report.

We can prevent this faulty behavior by specifying an "InputForm" that
prevebts the 2-dim output:
ToExpression[ToString[InputForm[1/3]]]
cheers, Daniel

Am 26.05.2010 13:09, schrieb James Stein:
> Evaluating:
>
> ToExpression [ ToString [ 1/3 ] ]
>
> I did not expect negative three!
>
> Bug? or a lack in my understanding?
>
>


--

Daniel Huber
Metrohm Ltd.
Oberdorfstr. 68
CH-9100 Herisau
Tel. +41 71 353 8585, Fax +41 71 353 8907
E-Mail:<mailto:dh(a)metrohm.com>
Internet:<http://www.metrohm.com>


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