How to get norm (magnitude) of a vector the simple way?

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Niklas Kurz 2021-5-4

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https://ww2.mathworks.cn/matlabcentral/answers/821685-how-to-get-norm-magnitude-of-a-vector-the-simple-way

编辑： Niklas Kurz 2021-5-8

采纳的回答： Nagasai Bharat

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I just want to get the norm of

syms phi the;
c = [-cos(phi)*sin(the)^2;-sin(phi)*sin(the)^2; - cos(the)*sin(the)*cos(phi)^2 - cos(the)*sin(the)*sin(phi)^2]

norm(c,2)

isn't really simplifying anything

If I type it manually:

simplify(sqrt(cos(phi)^2*sin(the)^4+sin(phi)^2*sin(the)^4+sin(the)^2*cos(the)^2))

I get a simple answere:

(sin(the)^2)^(1/2)

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David Goodmanson 2021-5-6

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Hi Niklas,

If your last two vector elements were

- cos(the)*sin(the)*cos(phi) - cos(the)*sin(the)*sin(phi)

i.e. cos(phi) and sin(phi) not squared, then you would get what you say. But since cos(phi) and sin(phi) are squared, you don't.

Niklas Kurz 2021-5-8

I'm sorry for forgetting the simicolons in c. It might have been hard for you to reproduce what I was trying to create.

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采纳的回答

Nagasai Bharat 2021-5-7

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Hi,

From the documentation of norm and simplify you could find the usage of both these functions. norm would be used to calculate the norm of a vector/matrix but not for an expression. simpify would be used in the simplification of an algebric expression.