RE: Comparison Error. Is ther
- To: mathgroup at smc.vnet.net
- Subject: [mg12714] RE: [mg12678] Comparison Error. Is ther
- From: Ersek_Ted%PAX1A at mr.nawcad.navy.mil
- Date: Wed, 3 Jun 1998 02:21:04 -0400
- Sender: owner-wri-mathgroup at wolfram.com
Chris wrote:
|
|I'm having trouble with comparisons, see below: |
|In[10]:= x=0.9;
| y=10;
|
|In[11]:= (1-x)y
|
|Out[11]=1.
|
|The above obviously evaluates to 1. |
|In[12]:= (1-x)y <1
|
|Out[12]= True
|
|The above gives the wrong answer.
|
|In[13]:= (1-x)y<1.
|
|Out[13]= False
|
|This gives the right answer, notice the decimal point after the 1. |
|
In the lines below I present a paradox somewhat related to the problem
above.
First I let (x) be a number near (-Pi/2) with eight digits of precision.
In[1]:=
x= -1.57079646`8;
y=Tan[x]
Out[2]=
0. x 10^6
(* Actually that's only the way it looks in a notebook. *)
I think the result in Out[2] means the number is on the order of 10^6,
but the leading digit is unknown. Now you get really strange results
for the tests below.
In[3]:=
x1=6630000;
{x1<r, r<x1}
Out[3]=
{False, False}
In[4]:=
x2=x1+1670000;
{x2<r, r<x2}
Out[4]=
{False, False}
In[5]:=
{
r==x1+100000,
r==x1+200000,
r==x1+300000,
r==x1+400000}
Out[5]=
{True, True, True, True}
What should we get for the results in Out[3], Out[4], Out[5] ? I think
we should get "Uncertain" when two numeric values are compared, and
we can't be certain that the result is True or False.
____________________
Ted Ersek