bug ?
- To: mathgroup at smc.vnet.net
- Subject: [mg122317] bug ?
- From: swiss <gregoire.nicollier at hevs.ch>
- Date: Tue, 25 Oct 2011 06:16:06 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
Following rational function has a double pole matched by a double root at (4+\sqrt{17})/4. The first result is correct, the other ones are false, but come without warning. Can somebody explain this to me?
In[50]:= Limit[-(((s (4 s - 5)^2 - (5 + 3 Sqrt[17])/
8 (4 s + 1)) ((4 s - 5)^2 -
4 (5 + 3 Sqrt[17])/8 (4 s - 7)))/(16 s^2 - 32 s - 1)^2),
s -> 1/4 (4 + Sqrt[17])]
Out[50]= 1/544 (331 - 19 Sqrt[17])
In[51]:= 1/544 (331 - 19 Sqrt[17]) // N
Out[51]= 0.46445
In[52]:= -(((s (4 s - 5)^2 - (5 + 3 Sqrt[17])/
8 (4 s + 1)) ((4 s - 5)^2 -
4 (5 + 3 Sqrt[17])/8 (4 s - 7)))/(16 s^2 - 32 s - 1)^2) /.
s -> 1/4 (4 + Sqrt[17]) // Simplify
Out[52]= 1/16 (1 + 2 Sqrt[17])
In[53]:= 1/16 (1 + 2 Sqrt[17]) // N
Out[53]= 0.577888
In[54]:= -(((s (4 s - 5)^2 - (5 + 3 Sqrt[17])/
8 (4 s + 1)) ((4 s - 5)^2 -
4 (5 + 3 Sqrt[17])/8 (4 s - 7)))/(16 s^2 - 32 s - 1)^2) /.
s -> 1/4 (4 + Sqrt[17.])
Out[54]= 0.09375
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