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Re: "Nice" complex form
*To*: mathgroup at smc.vnet.net
*Subject*: [mg131601] Re: "Nice" complex form
*From*: Bill Rowe <readnews at sbcglobal.net>
*Date*: Tue, 10 Sep 2013 03:35:28 -0400 (EDT)
*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com
*Delivered-to*: l-mathgroup@wolfram.com
*Delivered-to*: mathgroup-outx@smc.vnet.net
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On 9/9/13 at 12:06 AM, sam.takoy at yahoo.com wrote:
>Can I get
>Assuming[a - 4 < 0, Sqrt[a - 4]]
>to "simplify" to
>I Sqrt[4 - a]
Given Mathematica by default considers expressions with lower
LeafCount as simpler and:
In[1]:= Sqrt[a - 4] // LeafCount
Out[1]= 7
In[2]:= I Sqrt[4 - a] // LeafCount
Out[2]= 13
the simplest answer to your question is you can't, i.e., there
isn't a built-in function to do this. So, if you want to transform
Assuming[a - 4 < 0, Sqrt[a - 4]]
to
I Sqrt[4 - a]
you will have to create a special function to do that. Perhaps
the following will suffice:
In[3]:= Sqrt[a - 4] /. Sqrt[a_] -> I Sqrt[-a]
Out[3]= I*Sqrt[4 - a]
Or possibly you could add a transformation rule to Simplify. But
this last certainly seems counter to the design of Simplify.
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