Solve an equation of fourth degree with two variables

AAA
2013 5 22
1 个回答
回答已采纳
5 次查看（30 天）

0 个投票

I have to solve an equation of fourth degree with two variables, and draw the line where it is equal to zero. I tried to do that but I got an error message when I tried to place a value in x1_sol:
syms x y;
v=1/16*(3*x+17*y/3)*(-x^3-6*y^2-11*x+y)+1/96*(34*x+130*y)*/(3*x-y);
x_sol=solve(v==0,x,'MaxDegree', 4);
x1_sol=x_sol(1);
x1_sol(9);
Where am I wrong? Do I use the right way?

3 个评论
显示 1更早的评论 隐藏 1更早的评论

AAA
AAA 2013-5-23
编辑：AAA 2013-5-23
Error using mupadmex
Error in MuPAD command: Index exceeds matrix dimensions.
Error in sym/subsref (line 1577)
B = mupadmex('symobj::subsref',A.s,inds{:});
Error in Hw4 (line 7)
x1_sol(9);

请先登录，再进行评论。

请先登录，再回答此问题。

 采纳的回答

Valmir Sadiku
Valmir Sadiku 2013-5-23

0 个投票

i don't know what you are trying with this command x1_sol=x_sol(1); because the size of the x_sol are:
>> size(x_sol)
ans =
1 1
that's because it should be clear why x1_sol(9); give you an error message!

5 个评论
显示 3更早的评论 隐藏 3更早的评论

AAA
AAA 2013-5-23
I'm trying to set the parameter value Y to calculate X.
I want to calculate the value of X for a vector of Y. How do I do this?
Valmir Sadiku
Valmir Sadiku 2013-5-23
as far i understand you will solve this equation system:
v = 1/16*(3*x+17*y/3)*(-x^3-6*y^2-11*x+y)+1/96*(34*x+130*y)/(3*x-y);
y = 9;
if there so, you can do it in this way:
syms x y;
v=1/16*(3*x+17*y/3)*(-x^3-6*y^2-11*x+y)+1/96*(34*x+130*y)*/(3*x-y);
x_sol=solve(v==0, y ==9);
hopefully it will help you!
Walter Roberson
Walter Roberson 2013-5-23
Yvals = linspace(-10, 10, 101);
Xvals = double(subs(x_sol, y, Yvals));
Valmir Sadiku
Valmir Sadiku 2013-5-23
i never saw this command 'subs' bevor, so i think now you got the solution of your problem?
AAA
AAA 2013-5-24
编辑：AAA 2013-5-24
yes, it's exactly what I needed. thanks!

请先登录，再进行评论。

更多回答（0 个）

类别

在 帮助中心 和 File Exchange 中查找有关 Numeric Solvers 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by