Magnitude of a vector

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Philosophaie
Philosophaie 2013-9-5
评论： Steven Lord 2023-3-11
syms x y z
r = [x y z]
rmag???
rmag should equal (x^2 + y^2 + z^2)^0.5
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Prashant C
Prashant C 2015-6-3
use the function norm(r) or mag=sqrt(sum(r.*r))

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采纳的回答

Shashank Prasanna
编辑：MathWorks Support Team 2019-5-22
This works perfectly fine on MATLAB R2013a:
>> syms x y z
r = [x y z];
norm(r)
http://www.mathworks.com/help/symbolic/norm.html
  2 个评论
Shashank Prasanna
Shashank Prasanna 2013-9-5
编辑：MathWorks Support Team 2019-5-22
What version of MATLAB are you using? Can you confirm that you see the file when you run this:
>> which sym/norm
Bhuvana Krishnaraj
Bhuvana Krishnaraj 2019-6-3
2015.a version >>which sym/nom C:\matlab\toolbox\symbolic\@!sym\norm.m

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更多回答（2 个）

Azzi Abdelmalek
Azzi Abdelmalek 2013-9-5
m=sqrt(x^2+y^2+z^2)
Tariq Shajahan
Tariq Shajahan 2015-5-11
if 'r' is a vector. norm(r), gives the magnitude only if the vector has values. If r is an array of vectors, then the norm does not return the magnitude, rather the norm!!
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John D'Errico
John D'Errico 2023-3-11
Ran in:
If r is an array of vectors, what would you expect? How does MATLAB know, for example, that you want to compute the norm of each row of an array, as opposed to a matrix norm? In fact, when MATLAB is given a double precision array, and you use norm, it computes the MATRIX norm.
A = magic(5)
A = 5×5
17 24 1 8 15 23 5 7 14 16 4 6 13 20 22 10 12 19 21 3 11 18 25 2 9
norm(A)
ans = 65
There is no reason to expect it should instead compute the norm of each row, or each column. That would be wrong.
norm(sym(A))
ans = 
65
And norm is able to do the same thing for a symbolic array. So there should be no surprise here.
Steven Lord
Steven Lord 2023-3-11
Ran in:
To compute the norm of each row or column of a numeric matrix use vecnorm instead of norm.
A = magic(5);
vecnorm(A, 2, 1) % default 2-norm in dimension 1
ans = 1×5
32.4808 33.2415 34.7131 33.2415 32.4808
vecnorm(A, 1, 2) % 1-norm in dimension 2
ans = 5×1
65 65 65 65 65

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