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Replacing spurious Abs
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carlos.felipp...@gtempaccount.com
May 21, 2013, 12:02:13 AM5/21/13
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Hi,
Sometimes I get Abs[exp] from Simplify or Integrate, when it should be simply exp.
Is there a simple way to get rid of the Abs, when exp may be an arbitrarily
complex expression? Something like /.Abs[#]->#? Thanks.
Sometimes I get Abs[exp] from Simplify or Integrate, when it should be simply exp.
Is there a simple way to get rid of the Abs, when exp may be an arbitrarily
complex expression? Something like /.Abs[#]->#? Thanks.
Bill Rowe
May 21, 2013, 4:21:16 AM5/21/13
to
On 5/21/13 at 12:02 AM, carlos.felippa%colora...@gtempaccount.com
wrote:
In[1]:= Abs[exp] /. Abs[a_] -> a
Out[1]= exp
But keep in mind this is a literal syntax replacement which may
not be mathematically valid. That is you can do something like
In[2]:= Sqrt[2] /. Sqrt[a_] -> a
Out[2]= 2
Turning Sqrt[2] into 2 which is clearly not mathematically valid.
Another approach would be
In[3]:= Assuming[exp > 0, Simplify@Abs[exp]]
Out[3]= exp
which is a mathematically valid operation given the assumption
exp>0 is true. And this last can be done as:
In[4]:= Abs[exp] // Assuming[exp > 0, Simplify@#] &
Out[4]= exp
which is often handy
wrote:
Out[1]= exp
But keep in mind this is a literal syntax replacement which may
not be mathematically valid. That is you can do something like
In[2]:= Sqrt[2] /. Sqrt[a_] -> a
Out[2]= 2
Turning Sqrt[2] into 2 which is clearly not mathematically valid.
Another approach would be
In[3]:= Assuming[exp > 0, Simplify@Abs[exp]]
Out[3]= exp
which is a mathematically valid operation given the assumption
exp>0 is true. And this last can be done as:
In[4]:= Abs[exp] // Assuming[exp > 0, Simplify@#] &
Out[4]= exp
which is often handy
Bob Hanlon
May 21, 2013, 4:21:21 AM5/21/13
to
Abs[exp] /. Abs[x_] -> x
exp
or
Abs[exp] /. Abs -> Identity
exp
Bob Hanlon
On Tue, May 21, 2013 at 12:02 AM, <
carlos.felippa%colora...@gtempaccount.com> wrote:
> Hi,
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