Re: Chop in Mathematica 8.0.1

• To: mathgroup at smc.vnet.net
• Subject: [mg117552] Re: Chop in Mathematica 8.0.1
• From: telefunkenvf14 <rgorka at gmail.com>
• Date: Tue, 22 Mar 2011 05:09:25 -0500 (EST)
• References: <im7c6c\$74\$1@smc.vnet.net>

```On Mar 21, 6:18 am, Andrzej Kozlowski <a... at mimuw.edu.pl> wrote:
> Chop does not seem to work properly in Mathematica 8.0.1:
>
> f[a_] := 2 I Pi Sin[a]/a
>
> In[2]:= f[1.]
>
> Out[2]= 0. + 5.287118128162912*I
>
> In[3]:= Chop[%]
>
> Out[3]= 0. + 5.287118128162912*I
>
> This is with
>
> In[4]:= \$Version
>
> Out[4]= 8.0 for Mac OS X x86 (64-bit) (February 23, 2011)
>
>  Mathematica 7.01 returns 5.287118128162912*I as expected.
>
> Can anyone confirm it? At the moment I can't see any simple work around..  .
>
> Andrzej Kozlowski

I get the same behavior on Windows 7 for 7.0.1 and 8.0.1.

Did notice the documentation on Chop in 8.0.1 includes a new
subsection on 'possible issues'... Seems like there should be some
type of 'show changes' indicator in the documentation.

-------
>From the new subsection on possible issues:

Machine complex numbers have machine reals for both real and imaginary
parts:

In[1]:= 2. I
Out[1]= 0. + 2. I

Consequently, Chop does not make the real part of machine complex
numbers an exact zero:

In[2]:= Chop[10.^-12 + 2. I]
Out[2]= 0. + 2. I

Small imaginary parts from machine complex numbers are eliminated to
make a machine real:

In[3]:= Chop[2. + 10.^-12 I]
Out[3]= 2.

-----

It seems to me that 8.0.1 is the more desired behavior, no? (Maintains
precision; one can use Re or Im to select parts that remain, right?)

-RG

```

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