Finding Matrix A of Orthogonal Projection onto Line L in R2

In summary, to find the matrix A of the orthogonal projection onto the line L in R2 that consists of all scalar multiples of the vector [2 5]^T, you can use the formula 1/(1+m^2) [1 m; m m^2], where m is the slope of the line. In this case, the slope is 5/2, so the matrix would be 1/(1+25/4) [1 5/2; 5/2 25/4].
  • #1
sonya
23
0
Find the matrix A of the orthogonal projection onto the line L in R2 that consists of all scalar multiples of the vector [2 5]T .

OK...I really don't know how to start off with this problem. If somehow could just help me out there I will try to muddle my way through the rest ! Thanks.
 
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  • #2
OK...now I've thought about this...I should use the formula
1/(1+m2) [1 m ]
________[m m2]

using 2x+5y = 0 my slope m = -2/5

but my numbers come out backwards ...
 
  • #3
Your line is supposed to contain scalar multiples of [2 5]^T. Quick test-is [2 5]^T on the line 2x+5y = 0?
 
  • #4
ok...now I'm really lost! I thought I made an equation from the given vector...so what do I do instead ?
 
  • #5
You do make a line from the vector. Find two points on the line spanned by the vector, (0,0) and (2,5) will work. The y-intercept is therefore 0 and the slope is (5-0)/(2-0)=5/2. The line you gave has -2/5, so something was off.
 

Related to Finding Matrix A of Orthogonal Projection onto Line L in R2

1. What is the purpose of finding matrix A of orthogonal projection onto line L in R2?

The purpose of finding matrix A of orthogonal projection onto line L in R2 is to project a vector onto a line in two-dimensional space in a way that preserves the length and direction of the original vector. This can be useful in various mathematical and scientific applications, such as solving systems of linear equations or analyzing data in two-dimensional space.

2. How is matrix A of orthogonal projection onto line L in R2 calculated?

To calculate matrix A of orthogonal projection onto line L in R2, we first need to find the unit vector u that represents the direction of the line L. Then, we can use the formula A = uu^T, where u^T is the transpose of u, to find the projection matrix A. This matrix will have the dimensions of 2x2 and is unique for each line L in R2.

3. Can matrix A of orthogonal projection onto line L in R2 be used for lines in higher dimensions?

No, matrix A of orthogonal projection onto line L in R2 is specifically designed for lines in two-dimensional space. For lines in higher dimensions, we would need to use a different formula and a higher-dimensional matrix to represent the projection.

4. What is the relationship between matrix A of orthogonal projection onto line L in R2 and the dot product?

The matrix A of orthogonal projection onto line L in R2 is closely related to the dot product. In fact, the projection of a vector x onto a line L can be represented as the dot product of x and the unit vector u that represents the direction of the line. This means that A = uu^T is equivalent to the projection of x onto L.

5. Can matrix A of orthogonal projection onto line L in R2 be used for non-orthogonal lines?

No, the matrix A of orthogonal projection onto line L in R2 can only be used for orthogonal lines. If the line L is not orthogonal, we would need to use a different formula and a different matrix to represent the projection. However, we can still use the concept of projection to find the closest point on the line to a given vector in this case.

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