Re: Quartic
- To: mathgroup@smc.vnet.net
- Subject: [mg12535] Re: Quartic
- From: Colin L C Fu <es2136@eng.warwick.ac.uk>
- Date: Sat, 23 May 1998 18:11:01 -0400
- Organization: Warwick University
- References: <6jf5oh$47j@smc.vnet.net>
Colin L C Fu wrote:
>
> hiya,
>
> I want to solve 3 quartic eqns.
>
> Solve[{expr1, expr2, expr3 == 0}, A]
>
> As it is too long, I was advised to do the folowing:
>
> First, define the list of three expressions that you sent me before.
>
> _______________________________________
>
> In[1]:= expr = ...
> _______________________________________
>
> In[2]:= Short[e1 = First[expr], 5]
>
> Out[2]//Short=
>
> 4 3 8 4 2 2 4 2 4
> p1 (B + p2) q (q + q q2 (a + q2 ) + q2 (b + a q2 + q2 ))
> > --------------------------------------------------------------- + <<4>>
> 4
> q2
> _______________________________________
> _______________________________________
>
> In[3]:= ccoeffs =
> CoefficientList[c[1] + c[2] A + c[3] A^2 + c[4] A^3 + c[5] A^4,
> A]
>
> Out[3]= {c[1], c[2], c[3], c[4], c[5]}
> _______________________________________
> _______________________________________
>
> In[4]:= coefflist = CoefficientList[Collect[e1,A],A];
> _______________________________________
> _______________________________________
>
> In[5]:= sol = Solve[c[1] + c[2] A + c[3] A^2 + c[4] A^3 + c[5] A^4 == 0,
> A];
> _______________________________________
>
> _______________________________________
>
> In[6]:= InputForm[First[sol]]
>
> Out[6]//InputForm=
>
> {A -> -c[4]/(4*c[5]) - ...
>
> ---------------------------------------
>
> and Using this method, i manage to get the first solution of the 1st
> expression.
>
> If I want all the four solutions from the first quartic, I just type
>
> In[6]:= InputForm[sol], right?
>
> So I get all the four solutions. However, all the four solutions are
> the same in symbolic.
> This is not what I got when I just test the quartic by giving each
> variable in the quartic a value in which I used NSolve[expr,A].
>
> Why is that? Are all the four symbolic solutions that I got the correct
> answers?
>
> Please advise
>
> As I need to know the answer quit urgent, I have to post it to the
> newsgroup. However, I am in debt to those that been helping me too. I
> really appreciate it.
>
> Regards
> Col
--
It is solved at this stage now. Thanks for everybody that been giving
me advice.
Really appreciate it!
Cheerio
Col