Magnitude of a vector

syms x y z
r = [x y z]
rmag???

rmag should equal (x^2 + y^2 + z^2)^0.5

[Azzi Abdelmalek]

What is your question?

[Philosophaie]

I am looking for the magnitude of the vector r. It should be equal to r = (x^2 + y^2 + z^2)^0.5.

[Prashant C]

use the function norm(r) or mag=sqrt(sum(r.*r))

[Abdullraheem Diab]

Sqrt(sum(r.^2))

Answer 1

[Shashank Prasanna]

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

[Shashank Prasanna]

What version of MATLAB are you using? Can you confirm that you see the file when you run this:

>> which sym/norm

[Bhuvana Krishnaraj]

2015.a version >>which sym/nom C:\matlab\toolbox\symbolic\@!sym\norm.m

Answer 2

[Azzi Abdelmalek]

m=sqrt(x^2+y^2+z^2)

Answer 3

[Tariq Shajahan]

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!!

[John D'Errico]

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]

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