# How Do You Find a Matrix A Such That Y(t) Spirals Toward a Plane?

• djinteractive
In summary, the problem requires finding a matrix A that will cause the solution to Y'=AY, with initial condition Y(0)=(6,13,9), to spiral towards the plane 2x+3y+4z=0 and continue to circulate around a radius five circle. This can be achieved by finding vectors that span the plane and are orthogonal to it, and using them to compute the distance from Y(0) to the plane. The resulting curve is a "screw type" spiral, which can be expressed in a basis of (a,b,n). Using this basis, the matrix A can be found and the initial condition can be applied.
djinteractive
I am having trouble getting started with this problem.. I guess I'll explain it first.

Find one possible matrix A for which the solution to Y'=AY with initial condition Y(0)=(6,13,9) has the following property. As time progresses, the solution Y(t) spirals toward the plane 2x+3y+4z=0 where it continues to circultate about a radius five circle.

I know I have to find some vectors Vr(real) and Vi(imaginary) that span the plane and are orthogonal to it. The eigen vectors if I remember correctly should come in a pair Vr + iVi and Vr-iVi that I can normalize with PDP-1(inverse) but I am having a problem with how to get these eigenvalues that span the plane.. will someone PLEASE (I'm begging you) help me.. this is driving me insane
PS the 3rd (in z direction should just be a real lambda value I think)

A way to attack the problem could be :

Take a vector in the plane : a=(2,0,-1)/Sqrt(5), the normal vector to the plane : n=(2,3,4) and a vector in the plane, orthogonal to the first : b=(3,-10,6)/Sqrt(145).

Then you notice that you're LUCKY : you can easily compute the distance of Y(0) to the direction given by n : it is 5.

Hence the curve is not a 3d spiral but just a screw type one !

Hence you know that in the (a,b,n) basis, your vector expresses as :

x(t)=(5*cos(wt),5*sin(wt),A*exp(-Dt))

hence in the (a,b,n) basis : $$x'(t)=\left(\begin{array}{ccc} 0& -w & 0\\ w & 0 & 0\\0&0&-D\end{array}\right)x(t)$$

then you just have to change the basis to the canonical one and fit the initial condition.

First of all, don't panic! Solving this problem may seem daunting at first, but with a clear understanding of the concepts involved, you will be able to find a solution.

To start off, let's review the given information. We have a system of differential equations, Y' = AY, with an initial condition Y(0) = (6,13,9). We are looking for a matrix A that will cause the solution Y(t) to spiral towards the plane 2x+3y+4z=0 and continue to circulate about a radius five circle.

To achieve this, we need to find a matrix A that has eigenvalues that lie on the plane 2x+3y+4z=0. This means that the characteristic polynomial of A should have roots that satisfy this equation. In other words, the eigenvalues of A should be of the form λ = a+bi, where a and b are real numbers, and a+bi satisfies the equation 2x+3y+4z=0.

Now, let's consider the eigenvectors of A. Since A has complex eigenvalues, its eigenvectors will also be complex. However, we need real and imaginary eigenvectors that span the plane 2x+3y+4z=0 and are orthogonal to it. This means that we need to find two complex eigenvectors, Vr+iVi and Vr-iVi, where Vr and Vi are real vectors, that satisfy the following conditions:

1. They lie on the plane 2x+3y+4z=0.
2. They are orthogonal to the plane, i.e. their dot product with any vector on the plane is zero.

To find these eigenvectors, we can use the following steps:

1. Choose a random vector on the plane 2x+3y+4z=0, for example, (1,-2,1). This vector will be orthogonal to the plane.
2. Find the cross product of this vector with the normal vector of the plane, which is (2,3,4). This will give us a vector that lies on the plane and is orthogonal to the vector chosen in the previous step.
3. Normalize this vector to get Vr.
4. Set Vi as the cross product of Vr with the normal vector of the plane.

Now that we have our eigenvectors, we can construct

## 1. What is a 3D spiral?

A 3D spiral is a three-dimensional shape that curves and twists around a central axis in a repetitive pattern, creating a spiral effect.

## 2. How is a 3D spiral created?

A 3D spiral can be created using various software programs such as CAD or 3D modeling software. It can also be created by hand using materials such as wire or clay.

## 3. What are the applications of 3D spirals?

3D spirals have various applications in fields such as architecture, product design, and art. They can also be used in animations, visual effects, and virtual reality experiences.

## 4. Can 3D spirals be used for scientific purposes?

Yes, 3D spirals can be used in scientific studies and simulations to model various phenomena such as weather patterns, fluid dynamics, and DNA structures.

## 5. Are there any limitations to creating 3D spirals?

The main limitation in creating 3D spirals is the technology and software used. Some programs may have limitations on the complexity and size of the spiral that can be created. Additionally, creating physically large 3D spirals may require specialized equipment and materials.

• Engineering and Comp Sci Homework Help
Replies
18
Views
2K
• Precalculus Mathematics Homework Help
Replies
6
Views
1K
• Precalculus Mathematics Homework Help
Replies
2
Views
3K
• Calculus and Beyond Homework Help
Replies
5
Views
2K
Replies
2
Views
1K
• Precalculus Mathematics Homework Help
Replies
8
Views
2K
• Calculus and Beyond Homework Help
Replies
19
Views
3K
• Calculus and Beyond Homework Help
Replies
1
Views
1K
• Calculus and Beyond Homework Help
Replies
2
Views
2K
• Calculus and Beyond Homework Help
Replies
5
Views
1K