Polynomial arrays intersection and area within intersection

2014 8 9
2 个回答
回答已采纳
更新时间：2014 8 11
3 次查看（30 天）

0 个投票

Hello,
I don't understand what is meant by polynomial array. I am wondering if it is as simple as what I wrote.
For part 2, I know I need to do some sort of fzero, but I'm not really sure. like fzero(f1,f2) or something along those lines.

请先登录，再回答此问题。

 采纳的回答

Roger Stafford
Roger Stafford 2014-8-9

3 个投票

@Rick. What Ahmet has given you does in fact help. Your mistake lies in assuming powers for matlab's 'intersect' function that it doesn't have. If you read its documentation you will see what I mean. What you need at this point is 'roots', not 'intersect'. Does that get you going again?

8 个评论
显示 6更早的评论 隐藏 6更早的评论

Rick
Rick 2014-8-9
编辑：Rick 2014-8-9
Well, roots will find me the roots for the polynomial, however, I am trying to find where these two polynomials will intersect. I don't understand how to find where they will intersect. I did plot(x,polyval(f1,x)) and plot(x,polyval(f2,x)) and saw the two polynomials. I am convinced about polyval, I just don't know how to find the intersection using roots.
Roger Stafford
Roger Stafford 2014-8-9
You're so close to getting there it hurts! Think "difference", "difference", "difference"!
Rick
Rick 2014-8-10
roots(polyval(f1,x)-polyval(f2,x))?? That gives a large column array with imaginary numbers.
Roger Stafford
Roger Stafford 2014-8-10
That's not the way to get the coefficients of the difference between the polynomials. You're just getting the difference between their values that way. Think what 'roots' requires as an input.
Roger Stafford
Roger Stafford 2014-8-10
Rick, if you haven't solved your problem yet, ask yourself this question. What polynomial is it that has as its roots the three intersection points that are being sought, and what are its coefficients?
Rick
Rick 2014-8-10
I am still confused what it's supposed to be, I didn't understand your hint.
Roger Stafford
Roger Stafford 2014-8-11
Here is my final hint, Rick. What do you think would be the result of:
roots(f2-f1)
where f1 and f2 are the arrays referred to in part G.1 of your image.jpg ?
Rick
Rick 2014-8-11
apparently it gives you the intersection. I don't understand how it does that, I did that command and it gave the intersection.

请先登录，再进行评论。

更多回答（1 个）

Ahmet Cecen
Ahmet Cecen 2014-8-9

1 个投票

help polyval
And the rest is your homework. Good luck.

2 个评论
显示 无 隐藏 无

Rick
Rick 2014-8-9
编辑：Rick 2014-8-9
I don't see how that helps. I don't have values for x. One thing I would like to stress is that this is supposed to be done by hand, I wouldn't even have matlab with me since this was an exam problem.
is
f1 = [0 -0.5 -3.5 4];
f2 = [-0.1 0 1.3 5];
intersect(polyval(f2,x),polyval(f1,x))
ans =
Empty matrix: 1-by-0

请先登录，再进行评论。

类别

在 帮助中心 和 File Exchange 中查找有关 Polynomials 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