On Thu, Dec 10, 2009 at 12:45 AM, Mike Hansen <mhan...@gmail.com> wrote:
> On Thu, Dec 10, 2009 at 3:37 PM, ma...@mendelu.cz <ma...@mendelu.cz>
wrote:
>> sage: f = x + 3 < y - 2
>> sage: f*(-1)
>> -x - 3 < -y + 2
>>
>> Is this really intended behavior? Shouldnt the answer be the
>> following?
>>
>> sage: f*(-1)
>> -x - 3 > -y + 2
>>
>> But what about f*(a) or f*(x-2)? Should Sage return this?
>> (-x-3)*(x-2)<(2-y)*(x-2)
>
> I believe that this was indeed the intended behavior for the reasons
above.
Hmm. I remember when I first implemented inequalities that f*(-1) *did*
reverse the sign of the inequality, like Maple does:
> f := x+3 < y-2;
f := x < y - 5
> f*(-1);
-y + 5 < -x
I guess this was changed subsequently.
Mathematica does something weird and formal:
In[1]:= f := x+3 < y-2;
In[3]:= f*(-1)
Out[3]= -(3 + x < -2 + y)
-----
At this point, I'm just throwing some remarks out, not saying that we should
do anything in particular.
I'm curious -- who multiplies equalities by a scalar *except* high school
students or college students taking entry level college algebra classes?
William
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