Prev: Possible bug: Integrate[(u - t)*BesselY[0, 2*t], {t, 0, u}]
Next: Sorting nested lists
From: Sjoerd C. de Vries on 23 Mar 2010 05:21
Maria,

If you change the code as I described Mathematica reads infinity
(actually Infinity with a capital I) just fine, i.e. as a 'value' and
not as a string.

Simplify[var,Infinity] yields var as an answer, so it seems
Mathematica knows some transformation rules for Min, but it doesn't
seem to use this knowledge in situations as

Solve[{b == Min[c, d], d == Infinity}, {b}, {d}].

But even if it did, you would have problems solving the equations.
Your set contains, for instance,

consumerOinputPOTP == Min[consumerOoutputPOTP, consumerOTP],

where consumerOTP is not defined. (read a bullet for 'O')

If I ask you what the minimum of x and 5 is without specifying x, what
would you respond?

Cheers -- Sjoerd

On Mar 22, 9:46 am, Maria Davis <arbi...(a)gmail.com> wrote:
> > The Min of two unspecified variables cannot be reduced. Adding that
> > one of them equals Infinity doesn't help. The other might be the same.
>
> Hi Sjoerd;
>
> Thank you for your help.
> The equations presented in the file are the result of another
> software, I know that they contain much redunduncy, but I must resolve th=
em.
> For example, the given equations are:
> a=Min(c, d)
> c=infinity
>
> I want mathematica to solve the system above and returns a=d
> I don't understand why "Min" can not be reduced, so, please, is there
> any solution?
> I have also noticed that the term infinity is not understood as a
> value but as a string.
> Please I need your help.
> Thank you.


From: Bill Rowe on 23 Mar 2010 05:22
On 3/22/10 at 2:41 AM, arbiadr(a)gmail.com (Maria Davis) wrote:

>The equations presented in the file are the result of another software,
>I know that they contain much redunduncy, but I must resolve them. For
>example, the given equations are:

>a=Min(c, d)
>c=infinity

It is hard for me to determine whether you realize the above are
not equations in Mathematica or not. As equations, the above
would be:

a == Min[c,d]
c == Infinity

>I want mathematica to solve the system above and returns a=d I don't
>understand why "Min" can not be reduced, so, please, is there any
>solution?

Not without more information. The problem is d can be anything
including Infinity. Until d has a value that can be compared in
a useful manner with Infinity, Mathematica will correctly return
Min[d,Infinity] unevaluated as Min[d, Infinity] which is
obviously not what you want.

I can get Mathematica to do as you want doing the following:

In[1]:= eq1 = a == Min[c, d];
c = Infinity;

In[3]:= eq1 /. Min[a_, Infinity] :> a

Out[3]= a == d

Here, I've used Set (=) to set the value of c to Infinity. That
way, Mathematica's evaluator will replace all occurrences of c
with Infinity. Then I've used a replacement rule to transform
Min[d,Infinity] to d.

Note, when doing this last, I am no longer necessarily doing
valid mathematics. For example,

In[4]:= a + 1 /. b_ + _ :> b + 2

Out[4]= a+2

Demonstrating Mathematica will happily replace 1 with 2 using
replacement rules even though

In[5]:= 1 == 2

Out[5]= False


First  |  Prev  | 
Pages: 1 2
Prev: Possible bug: Integrate[(u - t)*BesselY[0, 2*t], {t, 0, u}]
Next: Sorting nested lists