[Date Index]
[Thread Index]
[Author Index]
Re: Taking LCM in a polynomial expression
*To*: mathgroup at smc.vnet.net
*Subject*: [mg95354] Re: Taking LCM in a polynomial expression
*From*: dh <dh at metrohm.com>
*Date*: Fri, 16 Jan 2009 06:10:14 -0500 (EST)
*References*: <gkn5pa$iob$1@smc.vnet.net>
Hi Srikanth,
the magic word to get a common denominator is: Together. E.g.:
Together[num1/den1 + num2/den1]
The second question is tougher. Mathematica orders increasingly by
default. You therefore have to prevent this by e.g. HoldForm. Try:
a2 x^2 + a1 x + a0
and
HoldForm[a2 x^2 + a1 x + a0]
Next question is how to get the polynomial inside HoldForm. Assume
p=a0 + a1 x + a2 x^2
a polynomial in default ordering. We may get its coefficients with
CoefficientList. The function Reverse reverses the coefficients list
cof=Reverse@CoefficientList[p, x]
the powers of x in our ordering:
pow=Table[x^i, {i, 2, 0, -1}]
The polynomial term in a list:
pol= cof pow
Now we insert pol into HoldForm by substitution and change List into Plus:
HoldForm[dummy]/.dummy->pol /. List->Plus
All together:
p=a0 + a1 x + a2 x^2;
cof=Reverse@CoefficientList[p, x];
pow=Table[x^i, {i, 2, 0, -1}];
pol= cof pow;
HoldForm[dummy]/.dummy->pol /. List->Plus
this gives:
a2 x^2+a1 x+a0
hope this helps, Daniel
Srikanth wrote:
> Hi
> I have a symbolic matrix that I invert. When I take each individual
> entry of the resulting matrix, I get an expression of the form:
> num1/den1 + num2/den1 + .... + num_n/den1
> where den1 is the determinant of the matrix. I'd like to get an
> expression of the form:
> Num/Den.
>
> I tried using Simplify (as well as multiplying the matrix by its
> determinant), but it doesn't seem to help. Any suggestions?
>
> On a related note, the final Num is a polynomial in two variables -
> say x,y. I'd like to arrange it in decreasing powers of x - like f1(y)
> x^n + f2(y) x^n-1... + constant. What function should use? Is there
> any way to both in a single step?
>
> Thanks a lot
> Srikanth
>
Prev by Date:
**Re: Problem in generating a DO cycle (mathematica 6.0)**
Next by Date:
**HowTo: Lookup Special Character names**
Previous by thread:
**Re: Taking LCM in a polynomial expression**
Next by thread:
**Taking LCM in a polynomial expression**
| |