Re: why doesn't the range on this interval match the plot range?
- To: mathgroup at smc.vnet.net
- Subject: [mg66431] Re: why doesn't the range on this interval match the plot range?
- From: Bill Rowe <readnewsciv at earthlink.net>
- Date: Fri, 12 May 2006 02:03:15 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
On 5/11/06 at 2:15 AM, chris at chiasson.name (Chris Chiasson) wrote:
>Parabola[x_]=4x^2+53x+160
>BeginPoint=-8;
>EndPoint=-5;
>Plot[Parabola[x],{x,BeginPoint,EndPoint}]
>Parabola[Interval[{BeginPoint,EndPoint}]]
Because Mathematica substitutes the entire interval for x to your function not just the interval end points. That is
In[26]:=
a=4Interval[{-8,-5}]^2
Out[26]=
Interval[{100,256}]
Note because of the minus sign, the result of Interval[{(-8}^2,(-5)^2}] is
Interval[{5^2, 8^2}]. That is for the first term, the end points are in "reverse" order from what you are expecting.
In[27]:=
b=53Interval[{-8,-5}]
Out[27]=
Interval[{-424,-265}]
In[28]:=
a+b+160
Out[28]=
Interval[{-164,151}]
while
In[29]:=
4x^2+53 x+160/.x\[Rule]-5
Out[29]=
-5
and
In[30]:=
4x^2+53 x+160/.x\[Rule]-8
Out[30]=
-8
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