- #1
degs2k4
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Hello,
I would like to check if my understanding of this linear algebra problem dealing with transformations is correct:
Part (1)
we have the following coordinates systems:
[tex] \tilde{x} = \begin{pmatrix} x_1 \\ x_2 \\ 1 \end{pmatrix} [/tex] and [tex] x = \begin{pmatrix} x_1 \\ x_2 \end{pmatrix} [/tex]
and the following equation : [tex] \tilde{x}^T \tilde{A} \tilde{x} = 0 [/tex]
This parts only asks for getting the A matrix (symmetric matrix with coefficients) from a quadratic curve. Taking a look at the final parts of the problem, I guess this part is some sort of coordinates change from [tex] \tilde{x} \rightarrow x [/tex] using a matrix A, is this right? (like some sort of 3D-2D transformation) Part (2)
we have the following coordinates systems:
[tex] x = \begin{pmatrix} x_1 \\ x_2 \end{pmatrix} [/tex] and [tex] y = \begin{pmatrix} y_1 \\ y_2 \end{pmatrix} [/tex]
and the following equation : [tex] x = Py [/tex]
My thoughts: The equation in (i) corresponds to a quadratic curve, which has been rotated (it has a cross product term) and translated (it has terms y1^2, y1). In this part we want to transform (i) into (ii). In this transformation we undo the rotation (by rotating) and the matrix used is for it is P, transforming x coords into y coords.
Part (3)
we have the following coordinates systems:
[tex] y = \begin{pmatrix} y_1 \\ y_2 \end{pmatrix} [/tex] and [tex] z = \begin{pmatrix} z_1 \\ z_2 \end{pmatrix} [/tex]
My thoughts: The equation in (ii) corresponds to a quadratic curve, which has been translated (it only has terms y1^2, y1). In this part we want to transform (ii) into (iii). In this transformation we undo the translation (by translating), with an equation like this:
[tex] z = y + M [/tex]
transforming coords y into coords z. Part (4.A)
we have the following coordinates systems:
[tex] z = \begin{pmatrix} z_1 \\ z_2 \end{pmatrix} [/tex] and [tex] \tilde{z} = \begin{pmatrix} z_1 \\ z_2 \\ 1 \end{pmatrix} [/tex]
and the following equation : [tex] \tilde{z}^T \tilde{B} \tilde{z} = 0 [/tex]
This parts looks like part 1, getting the matrix from a quadratic curve. Taking a look at the rest of the parts of the problem, I guess this part is a coordinates change from [tex] z \rightarrow \tilde{z} [/tex] using a matrix B, is this right? Part (4.B)
we have the following coordinates systems:
[tex] \tilde{z} = \begin{pmatrix} z_1 \\ z_2 \\ 1 \end{pmatrix} [/tex] and [tex] \tilde{x} = \begin{pmatrix} x_1 \\ x_2 \\ 1 \end{pmatrix} [/tex]
and the following equation : [tex] \tilde{x} = \tilde{Q} \tilde{z} [/tex]
This part is the composite transformation from (i), using coords [tex] \tilde{x} [/tex] to (iii) using coords [tex] \tilde{z} [/tex]. So composing all transformations from the previous parts into one, my guess is that :
[tex] \tilde{Q} = ((\tilde{A} P) + M)\tilde{B} [/tex]
would this be ok?
Thanks in advance and sorry for the long post...
I would like to check if my understanding of this linear algebra problem dealing with transformations is correct:
Part (1)
we have the following coordinates systems:
[tex] \tilde{x} = \begin{pmatrix} x_1 \\ x_2 \\ 1 \end{pmatrix} [/tex] and [tex] x = \begin{pmatrix} x_1 \\ x_2 \end{pmatrix} [/tex]
and the following equation : [tex] \tilde{x}^T \tilde{A} \tilde{x} = 0 [/tex]
This parts only asks for getting the A matrix (symmetric matrix with coefficients) from a quadratic curve. Taking a look at the final parts of the problem, I guess this part is some sort of coordinates change from [tex] \tilde{x} \rightarrow x [/tex] using a matrix A, is this right? (like some sort of 3D-2D transformation) Part (2)
we have the following coordinates systems:
[tex] x = \begin{pmatrix} x_1 \\ x_2 \end{pmatrix} [/tex] and [tex] y = \begin{pmatrix} y_1 \\ y_2 \end{pmatrix} [/tex]
and the following equation : [tex] x = Py [/tex]
My thoughts: The equation in (i) corresponds to a quadratic curve, which has been rotated (it has a cross product term) and translated (it has terms y1^2, y1). In this part we want to transform (i) into (ii). In this transformation we undo the rotation (by rotating) and the matrix used is for it is P, transforming x coords into y coords.
Part (3)
we have the following coordinates systems:
[tex] y = \begin{pmatrix} y_1 \\ y_2 \end{pmatrix} [/tex] and [tex] z = \begin{pmatrix} z_1 \\ z_2 \end{pmatrix} [/tex]
My thoughts: The equation in (ii) corresponds to a quadratic curve, which has been translated (it only has terms y1^2, y1). In this part we want to transform (ii) into (iii). In this transformation we undo the translation (by translating), with an equation like this:
[tex] z = y + M [/tex]
transforming coords y into coords z. Part (4.A)
we have the following coordinates systems:
[tex] z = \begin{pmatrix} z_1 \\ z_2 \end{pmatrix} [/tex] and [tex] \tilde{z} = \begin{pmatrix} z_1 \\ z_2 \\ 1 \end{pmatrix} [/tex]
and the following equation : [tex] \tilde{z}^T \tilde{B} \tilde{z} = 0 [/tex]
This parts looks like part 1, getting the matrix from a quadratic curve. Taking a look at the rest of the parts of the problem, I guess this part is a coordinates change from [tex] z \rightarrow \tilde{z} [/tex] using a matrix B, is this right? Part (4.B)
we have the following coordinates systems:
[tex] \tilde{z} = \begin{pmatrix} z_1 \\ z_2 \\ 1 \end{pmatrix} [/tex] and [tex] \tilde{x} = \begin{pmatrix} x_1 \\ x_2 \\ 1 \end{pmatrix} [/tex]
and the following equation : [tex] \tilde{x} = \tilde{Q} \tilde{z} [/tex]
This part is the composite transformation from (i), using coords [tex] \tilde{x} [/tex] to (iii) using coords [tex] \tilde{z} [/tex]. So composing all transformations from the previous parts into one, my guess is that :
[tex] \tilde{Q} = ((\tilde{A} P) + M)\tilde{B} [/tex]
would this be ok?
Thanks in advance and sorry for the long post...