Simple, construct a basis of R2 with an inner product

In summary, the conversation involves constructing an orthogonal basis for R2 with a non-standard inner product defined by <X,Y> = X^T AY, where A is a given matrix. The individual attempts at solving this problem involve using the canonical basis of R2 and solving equations for arbitrary vectors, but the solution only works when both points are non-zero. The final solution obtained is ( 1 - [1+sqrt(5)]/2 , [1+sqrt(5)]/2 ) and (1, 1) which seem to be linearly independent.
  • #1
simpledude
21
0

Homework Statement


Construct an orthogonal basis of R2 equipped with the non-standard inner product defined for all X, Y belonging to R2, by

<X,Y> = X^T AY
with
A =
2 1
1 3

The Attempt at a Solution


So it seems pretty trivial, but I can't seem to get the answer. So my approach is
1) First get any basis that fits with this inner product
2) Use Gram-Scmidt to orthogonalize that basis

So I know I can start with the canonical basis of R2: (1,0) (0,1)
My problem is, how can I satisfy the inner product if I start from the canonical basis?

I have also attempted to solve the equations of two arbitrary vectors v1, v2
where v1=(x1, y2) and v2=(x2,y2) and given the matrix A we know:
x1x2 + y1y2 = 1
x1^2 + y1^2 = 2
x2^2 + y2^2 = 3
But if I plug in the canoical basis for v1, the solution fails. It only works when both points are non-zero, i.e. v1 = (1, 1)Any help would be appreciated.

EDIT:
Actually now that I am looking at my solution, I obtained (via my method of substituting (1,1) for x1, y1 in my equations) the basis that works with this inner product as:
( 1 - [1+sqrt(5)]/2 , [1+sqrt(5)]/2 ) and (1, 1)

They seem to be linearly independent, did I do this right? (I know I still have to orthogonalize them)
 
Last edited:
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  • #2
Anyone?
 

Related to Simple, construct a basis of R2 with an inner product

1. What is a basis in mathematics?

A basis is a set of vectors that can be used to represent all other vectors in a given vector space. It is similar to the concept of coordinates in geometry, where a set of coordinates can be used to represent any point in a plane.

2. Can you explain what an inner product is?

An inner product is a mathematical operation that takes two vectors as inputs and produces a scalar value as an output. It is often used to measure the angle between two vectors or the length of a vector.

3. How do you construct a basis in R2?

To construct a basis in R2, you need to find two linearly independent vectors. This means that the two vectors are not multiples of each other and can span the entire R2 space. For example, the vectors (1,0) and (0,1) can form a basis in R2.

4. What is the importance of having a basis in R2?

A basis in R2 is important because it allows us to represent any vector in R2 using a linear combination of the basis vectors. This makes it easier to perform mathematical operations and transformations on vectors in R2.

5. Can you give an example of constructing a basis in R2 with an inner product?

Yes, an example of constructing a basis in R2 with an inner product is using the vectors (1,0) and (0,1). The inner product of these two vectors is 0, indicating that they are orthogonal. Therefore, these two vectors can form a basis for R2 with the inner product defined as the dot product.

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