市川 雄二
ichik****@gmail*****
2013年 2月 24日 (日) 20:45:09 JST
# Cc:だとこちらに届かないんでしょうか？ 以下のメールを本家メーリングリストに出してみました。 ー 市川雄二 Begin forwarded message: > 差出人: 市川 雄二 <ichik****@gmail*****> > 件名: Solving 3rd order equation by solve. > 日時: 2013年2月24日 20:24:46 JST > 宛先: Maxim****@math***** > Cc: "maxim****@lists*****" <maxim****@lists*****> > > Hi. > > I have a question about solving 3rd order equation by solve. > > Executing > solution: solve(x^3-x^2+1=0, x), rectform; > results > [x=(1/(2*3^(3/2)*(25/54-sqrt(23)/(2*3^(3/2)))^(1/3))-(sqrt(3)*(25/54-sqrt(23)/(2*3^(3/2)))^(1/3))/2)*%i+(25/54-sqrt(23)/(2*3^(3/2)))^(1/3)/2+1/(18*(25/54-sqrt(23)/(2*3^(3/2)))^(1/3))+1/3, > x=-(25/54-sqrt(23)/(2*3^(3/2)))^(1/3)-1/(9*(25/54-sqrt(23)/(2*3^(3/2)))^(1/3))+1/3, > x=((sqrt(3)*(25/54-sqrt(23)/(2*3^(3/2)))^(1/3))/2-1/(2*3^(3/2)*(25/54-sqrt(23)/(2*3^(3/2)))^(1/3)))*%i+(25/54-sqrt(23)/(2*3^(3/2)))^(1/3)/2+1/(18*(25/54-sqrt(23)/(2*3^(3/2)))^(1/3))+1/3]. > > The second one in solution is a real root. > To know the concrete value, executing > solution, float; > results > [x=0.744861766619749*%i+.8774388331233485,x=-.7548776662466969,x=.8774388331233485-0.744861766619749*%i]. > > I want to get this result by single command. > But executing > solution: solve(x^3-x^2+1=0, x), rectform, float; > results > [x=.7448617666197254*%i+.8774388331233376,x=-8.480870326997723*10^-17*%i-.7548776662466756,x=.8774388331233378- > .7448617666197253*%i]. > > The second one includes a very small imaginary part. > > How can I avoid it? > # I tried realroots and knew it gives me a value. But I want to know how to use solve command. > > My environment is, > Mac OS X 10.8.2 > maxima 5.28.0 from http://sourceforge.net/projects/maxima/files/ > > Thanks, > - > ICHIKAWA, Yuji > > -------------- next part -------------- HTMLの添付ファイルを保管しました...下載
