Orthogonal Matrix with a specific row
I have an assignment with the following question:
Does an Orthogonal Matrix exist such that its first row consists of the
following values:
($1$/$sqrt{3}$, $1$/$sqrt{3}$, $1$/$sqrt{3}$)
If there is, find one.
I know I can solve this question with the Gram Schmidt algorithm, but it includes a lot of complicated calculations.
Is there any other way to prove this statement without the Gram Schmidt algorithm?
Thanks,
Alan
linear-algebra orthonormal orthogonality
add a comment |
I have an assignment with the following question:
Does an Orthogonal Matrix exist such that its first row consists of the
following values:
($1$/$sqrt{3}$, $1$/$sqrt{3}$, $1$/$sqrt{3}$)
If there is, find one.
I know I can solve this question with the Gram Schmidt algorithm, but it includes a lot of complicated calculations.
Is there any other way to prove this statement without the Gram Schmidt algorithm?
Thanks,
Alan
linear-algebra orthonormal orthogonality
There is another way. You should be able to show that each row (column) of an orthogonal matrix is orthonormal to the other rows (columns) of the matrix. That fact should be enough to answer the original question.
– LouisB
Nov 23 '14 at 6:32
@Louis, can you please elaborate, as I amnot sure how to prove that? Thank you in advance.
– Alan
Nov 23 '14 at 6:34
I misread the question! I managed to read $1, {sqrt{3}}$ instead of $1/{sqrt{3}}$. Sorry about that.
– LouisB
Nov 23 '14 at 7:01
Similar: math.stackexchange.com/questions/2241414/….
– StubbornAtom
May 7 '17 at 10:56
An orthogonal matrix will have mutually perpendicular rows of unit vectors so as long as the vector is a unit vector you're have sufficient conditions for the existence of such a matrix.
– CyclotomicField
Jul 2 '18 at 4:31
add a comment |
I have an assignment with the following question:
Does an Orthogonal Matrix exist such that its first row consists of the
following values:
($1$/$sqrt{3}$, $1$/$sqrt{3}$, $1$/$sqrt{3}$)
If there is, find one.
I know I can solve this question with the Gram Schmidt algorithm, but it includes a lot of complicated calculations.
Is there any other way to prove this statement without the Gram Schmidt algorithm?
Thanks,
Alan
linear-algebra orthonormal orthogonality
I have an assignment with the following question:
Does an Orthogonal Matrix exist such that its first row consists of the
following values:
($1$/$sqrt{3}$, $1$/$sqrt{3}$, $1$/$sqrt{3}$)
If there is, find one.
I know I can solve this question with the Gram Schmidt algorithm, but it includes a lot of complicated calculations.
Is there any other way to prove this statement without the Gram Schmidt algorithm?
Thanks,
Alan
linear-algebra orthonormal orthogonality
linear-algebra orthonormal orthogonality
edited Nov 23 '14 at 6:27
asked Nov 23 '14 at 6:13
Alan
1,3671021
1,3671021
There is another way. You should be able to show that each row (column) of an orthogonal matrix is orthonormal to the other rows (columns) of the matrix. That fact should be enough to answer the original question.
– LouisB
Nov 23 '14 at 6:32
@Louis, can you please elaborate, as I amnot sure how to prove that? Thank you in advance.
– Alan
Nov 23 '14 at 6:34
I misread the question! I managed to read $1, {sqrt{3}}$ instead of $1/{sqrt{3}}$. Sorry about that.
– LouisB
Nov 23 '14 at 7:01
Similar: math.stackexchange.com/questions/2241414/….
– StubbornAtom
May 7 '17 at 10:56
An orthogonal matrix will have mutually perpendicular rows of unit vectors so as long as the vector is a unit vector you're have sufficient conditions for the existence of such a matrix.
– CyclotomicField
Jul 2 '18 at 4:31
add a comment |
There is another way. You should be able to show that each row (column) of an orthogonal matrix is orthonormal to the other rows (columns) of the matrix. That fact should be enough to answer the original question.
– LouisB
Nov 23 '14 at 6:32
@Louis, can you please elaborate, as I amnot sure how to prove that? Thank you in advance.
– Alan
Nov 23 '14 at 6:34
I misread the question! I managed to read $1, {sqrt{3}}$ instead of $1/{sqrt{3}}$. Sorry about that.
– LouisB
Nov 23 '14 at 7:01
Similar: math.stackexchange.com/questions/2241414/….
– StubbornAtom
May 7 '17 at 10:56
An orthogonal matrix will have mutually perpendicular rows of unit vectors so as long as the vector is a unit vector you're have sufficient conditions for the existence of such a matrix.
– CyclotomicField
Jul 2 '18 at 4:31
There is another way. You should be able to show that each row (column) of an orthogonal matrix is orthonormal to the other rows (columns) of the matrix. That fact should be enough to answer the original question.
– LouisB
Nov 23 '14 at 6:32
There is another way. You should be able to show that each row (column) of an orthogonal matrix is orthonormal to the other rows (columns) of the matrix. That fact should be enough to answer the original question.
– LouisB
Nov 23 '14 at 6:32
@Louis, can you please elaborate, as I amnot sure how to prove that? Thank you in advance.
– Alan
Nov 23 '14 at 6:34
@Louis, can you please elaborate, as I amnot sure how to prove that? Thank you in advance.
– Alan
Nov 23 '14 at 6:34
I misread the question! I managed to read $1, {sqrt{3}}$ instead of $1/{sqrt{3}}$. Sorry about that.
– LouisB
Nov 23 '14 at 7:01
I misread the question! I managed to read $1, {sqrt{3}}$ instead of $1/{sqrt{3}}$. Sorry about that.
– LouisB
Nov 23 '14 at 7:01
Similar: math.stackexchange.com/questions/2241414/….
– StubbornAtom
May 7 '17 at 10:56
Similar: math.stackexchange.com/questions/2241414/….
– StubbornAtom
May 7 '17 at 10:56
An orthogonal matrix will have mutually perpendicular rows of unit vectors so as long as the vector is a unit vector you're have sufficient conditions for the existence of such a matrix.
– CyclotomicField
Jul 2 '18 at 4:31
An orthogonal matrix will have mutually perpendicular rows of unit vectors so as long as the vector is a unit vector you're have sufficient conditions for the existence of such a matrix.
– CyclotomicField
Jul 2 '18 at 4:31
add a comment |
3 Answers
3
active
oldest
votes
You need to choose two vectors which are orthogonal to $left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)$ and make sure they are also orthogonal to each other.
Vectors orthogonal to $left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)$ lie in the plane $x+y+z=0$.
For example choose $(1,-1,0)$ to be the second row of your matrix.
Now you need a third vector which satisfies the equations:
$$x+y+z=0 ~~~ text{[is orthogonal to}~left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)]$$
$$x-y=0 ~~~ text{[is orthogonal to}~(1,-1,0)]$$
Any such vector can form the third row of your orthogonal matrix.
One way to find a 3rd vector is to take the cross product of the first two vectors.
– Gerry Myerson
Nov 23 '14 at 10:57
add a comment |
i answered a similar question before, but i don't know how to make a link to that.
so i will repeat the way to find a symmetric reflection matrix whose row is your unit vector. reflect $((1,1,1)^T/sqrt 3$ to $(1,0,0)^T$ on the mirror in the direction of their bisector $a = (1 + sqrt 3, 1, 1)^T.$ form the matrix $q = 2aa^T/a^Ta - I;$ that will satisfy your requirement.
add a comment |
$(frac1{sqrt3},frac1{sqrt3},frac1{sqrt3})$ is a unit vector, so you're off to a good start. (That is, there is such a matrix.)
Next just choose a perpendicular vector, and normalize it. So, say, $(frac1{sqrt2},-frac1{sqrt2},0)$.
Finally you need a vector perpendicular to the first two, and again of unit length. The cross-product will produce such a vector. Or, looking at the first two, I think I can produce one out of the blue. Namely, $(frac1{sqrt6},frac1{sqrt6},-frac2{sqrt6})$. You can easily check that the dot products with the other two vectors are zero. And it has unit length.
So one such matrix is: $$begin{pmatrix}frac1{sqrt3}& frac1{sqrt3}& frac1{sqrt3}\frac1{sqrt2}&-frac1{sqrt2}&0\frac1{sqrt6}&frac1{sqrt6}&-frac2{sqrt6}end{pmatrix}$$.
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "69"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f1034698%2forthogonal-matrix-with-a-specific-row%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
You need to choose two vectors which are orthogonal to $left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)$ and make sure they are also orthogonal to each other.
Vectors orthogonal to $left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)$ lie in the plane $x+y+z=0$.
For example choose $(1,-1,0)$ to be the second row of your matrix.
Now you need a third vector which satisfies the equations:
$$x+y+z=0 ~~~ text{[is orthogonal to}~left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)]$$
$$x-y=0 ~~~ text{[is orthogonal to}~(1,-1,0)]$$
Any such vector can form the third row of your orthogonal matrix.
One way to find a 3rd vector is to take the cross product of the first two vectors.
– Gerry Myerson
Nov 23 '14 at 10:57
add a comment |
You need to choose two vectors which are orthogonal to $left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)$ and make sure they are also orthogonal to each other.
Vectors orthogonal to $left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)$ lie in the plane $x+y+z=0$.
For example choose $(1,-1,0)$ to be the second row of your matrix.
Now you need a third vector which satisfies the equations:
$$x+y+z=0 ~~~ text{[is orthogonal to}~left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)]$$
$$x-y=0 ~~~ text{[is orthogonal to}~(1,-1,0)]$$
Any such vector can form the third row of your orthogonal matrix.
One way to find a 3rd vector is to take the cross product of the first two vectors.
– Gerry Myerson
Nov 23 '14 at 10:57
add a comment |
You need to choose two vectors which are orthogonal to $left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)$ and make sure they are also orthogonal to each other.
Vectors orthogonal to $left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)$ lie in the plane $x+y+z=0$.
For example choose $(1,-1,0)$ to be the second row of your matrix.
Now you need a third vector which satisfies the equations:
$$x+y+z=0 ~~~ text{[is orthogonal to}~left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)]$$
$$x-y=0 ~~~ text{[is orthogonal to}~(1,-1,0)]$$
Any such vector can form the third row of your orthogonal matrix.
You need to choose two vectors which are orthogonal to $left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)$ and make sure they are also orthogonal to each other.
Vectors orthogonal to $left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)$ lie in the plane $x+y+z=0$.
For example choose $(1,-1,0)$ to be the second row of your matrix.
Now you need a third vector which satisfies the equations:
$$x+y+z=0 ~~~ text{[is orthogonal to}~left(frac{1}{sqrt{3}},frac{1}{sqrt{3}},frac{1}{sqrt{3}}right)]$$
$$x-y=0 ~~~ text{[is orthogonal to}~(1,-1,0)]$$
Any such vector can form the third row of your orthogonal matrix.
answered Nov 23 '14 at 6:39
RHP
1,40811525
1,40811525
One way to find a 3rd vector is to take the cross product of the first two vectors.
– Gerry Myerson
Nov 23 '14 at 10:57
add a comment |
One way to find a 3rd vector is to take the cross product of the first two vectors.
– Gerry Myerson
Nov 23 '14 at 10:57
One way to find a 3rd vector is to take the cross product of the first two vectors.
– Gerry Myerson
Nov 23 '14 at 10:57
One way to find a 3rd vector is to take the cross product of the first two vectors.
– Gerry Myerson
Nov 23 '14 at 10:57
add a comment |
i answered a similar question before, but i don't know how to make a link to that.
so i will repeat the way to find a symmetric reflection matrix whose row is your unit vector. reflect $((1,1,1)^T/sqrt 3$ to $(1,0,0)^T$ on the mirror in the direction of their bisector $a = (1 + sqrt 3, 1, 1)^T.$ form the matrix $q = 2aa^T/a^Ta - I;$ that will satisfy your requirement.
add a comment |
i answered a similar question before, but i don't know how to make a link to that.
so i will repeat the way to find a symmetric reflection matrix whose row is your unit vector. reflect $((1,1,1)^T/sqrt 3$ to $(1,0,0)^T$ on the mirror in the direction of their bisector $a = (1 + sqrt 3, 1, 1)^T.$ form the matrix $q = 2aa^T/a^Ta - I;$ that will satisfy your requirement.
add a comment |
i answered a similar question before, but i don't know how to make a link to that.
so i will repeat the way to find a symmetric reflection matrix whose row is your unit vector. reflect $((1,1,1)^T/sqrt 3$ to $(1,0,0)^T$ on the mirror in the direction of their bisector $a = (1 + sqrt 3, 1, 1)^T.$ form the matrix $q = 2aa^T/a^Ta - I;$ that will satisfy your requirement.
i answered a similar question before, but i don't know how to make a link to that.
so i will repeat the way to find a symmetric reflection matrix whose row is your unit vector. reflect $((1,1,1)^T/sqrt 3$ to $(1,0,0)^T$ on the mirror in the direction of their bisector $a = (1 + sqrt 3, 1, 1)^T.$ form the matrix $q = 2aa^T/a^Ta - I;$ that will satisfy your requirement.
answered Nov 23 '14 at 15:50
abel
26.5k11948
26.5k11948
add a comment |
add a comment |
$(frac1{sqrt3},frac1{sqrt3},frac1{sqrt3})$ is a unit vector, so you're off to a good start. (That is, there is such a matrix.)
Next just choose a perpendicular vector, and normalize it. So, say, $(frac1{sqrt2},-frac1{sqrt2},0)$.
Finally you need a vector perpendicular to the first two, and again of unit length. The cross-product will produce such a vector. Or, looking at the first two, I think I can produce one out of the blue. Namely, $(frac1{sqrt6},frac1{sqrt6},-frac2{sqrt6})$. You can easily check that the dot products with the other two vectors are zero. And it has unit length.
So one such matrix is: $$begin{pmatrix}frac1{sqrt3}& frac1{sqrt3}& frac1{sqrt3}\frac1{sqrt2}&-frac1{sqrt2}&0\frac1{sqrt6}&frac1{sqrt6}&-frac2{sqrt6}end{pmatrix}$$.
add a comment |
$(frac1{sqrt3},frac1{sqrt3},frac1{sqrt3})$ is a unit vector, so you're off to a good start. (That is, there is such a matrix.)
Next just choose a perpendicular vector, and normalize it. So, say, $(frac1{sqrt2},-frac1{sqrt2},0)$.
Finally you need a vector perpendicular to the first two, and again of unit length. The cross-product will produce such a vector. Or, looking at the first two, I think I can produce one out of the blue. Namely, $(frac1{sqrt6},frac1{sqrt6},-frac2{sqrt6})$. You can easily check that the dot products with the other two vectors are zero. And it has unit length.
So one such matrix is: $$begin{pmatrix}frac1{sqrt3}& frac1{sqrt3}& frac1{sqrt3}\frac1{sqrt2}&-frac1{sqrt2}&0\frac1{sqrt6}&frac1{sqrt6}&-frac2{sqrt6}end{pmatrix}$$.
add a comment |
$(frac1{sqrt3},frac1{sqrt3},frac1{sqrt3})$ is a unit vector, so you're off to a good start. (That is, there is such a matrix.)
Next just choose a perpendicular vector, and normalize it. So, say, $(frac1{sqrt2},-frac1{sqrt2},0)$.
Finally you need a vector perpendicular to the first two, and again of unit length. The cross-product will produce such a vector. Or, looking at the first two, I think I can produce one out of the blue. Namely, $(frac1{sqrt6},frac1{sqrt6},-frac2{sqrt6})$. You can easily check that the dot products with the other two vectors are zero. And it has unit length.
So one such matrix is: $$begin{pmatrix}frac1{sqrt3}& frac1{sqrt3}& frac1{sqrt3}\frac1{sqrt2}&-frac1{sqrt2}&0\frac1{sqrt6}&frac1{sqrt6}&-frac2{sqrt6}end{pmatrix}$$.
$(frac1{sqrt3},frac1{sqrt3},frac1{sqrt3})$ is a unit vector, so you're off to a good start. (That is, there is such a matrix.)
Next just choose a perpendicular vector, and normalize it. So, say, $(frac1{sqrt2},-frac1{sqrt2},0)$.
Finally you need a vector perpendicular to the first two, and again of unit length. The cross-product will produce such a vector. Or, looking at the first two, I think I can produce one out of the blue. Namely, $(frac1{sqrt6},frac1{sqrt6},-frac2{sqrt6})$. You can easily check that the dot products with the other two vectors are zero. And it has unit length.
So one such matrix is: $$begin{pmatrix}frac1{sqrt3}& frac1{sqrt3}& frac1{sqrt3}\frac1{sqrt2}&-frac1{sqrt2}&0\frac1{sqrt6}&frac1{sqrt6}&-frac2{sqrt6}end{pmatrix}$$.
answered Jan 2 at 7:29
Chris Custer
10.9k3824
10.9k3824
add a comment |
add a comment |
Thanks for contributing an answer to Mathematics Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f1034698%2forthogonal-matrix-with-a-specific-row%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
There is another way. You should be able to show that each row (column) of an orthogonal matrix is orthonormal to the other rows (columns) of the matrix. That fact should be enough to answer the original question.
– LouisB
Nov 23 '14 at 6:32
@Louis, can you please elaborate, as I amnot sure how to prove that? Thank you in advance.
– Alan
Nov 23 '14 at 6:34
I misread the question! I managed to read $1, {sqrt{3}}$ instead of $1/{sqrt{3}}$. Sorry about that.
– LouisB
Nov 23 '14 at 7:01
Similar: math.stackexchange.com/questions/2241414/….
– StubbornAtom
May 7 '17 at 10:56
An orthogonal matrix will have mutually perpendicular rows of unit vectors so as long as the vector is a unit vector you're have sufficient conditions for the existence of such a matrix.
– CyclotomicField
Jul 2 '18 at 4:31