norm of vector with cosine(var)

Question

Arne Kähler 2021-2-20

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/751514-norm-of-vector-with-cosine-var

回答： Arne Kähler 2021-2-21

采纳的回答： Arne Kähler

在 MATLAB Online 中打开

How can I calculate the norm of a vector which is of form [sin(t);cos(t)]?

I tried

f=x*y^2;gamma=[2*cos(t);sin(t)];tmin=0;tmax=2*pi;
mod=matlabFunction(norm(dgamma))
value=int((fgamma)*mod,t,tmin,tmax)

with answer

mod =
  function_handle with value:
    @(t)sqrt(abs(cos(t)).^2+abs(sin(t)).^2.*4.0)
value =  int(2*cos(t)*sin(t)^2*(abs(cos(t))^2 + 4*abs(sin(t))^2)^(1/2), t, 0, 2*pi)

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Arne Kähler 2021-2-21

在 MATLAB Online 中打开

That was an example @John D'Errico...

It's an unknown function handle put in by the user but my function had issues with calculating the euclidian Norm of a vector when theres cosine or sine in it, that's why I used the example.

I solved it by a simple workaround:

mod=0;
for k=1:nargin(f)
   mod=mod+dgamma(k)^2;
end
    mod=sqrt(mod);
    integr=sym((fgamma)*mod)
    value=int(integr,tmin,tmax)

John D'Errico 2021-2-21

编辑：John D'Errico 2021-2-21

Ok, so you have a more complex vector. I would note that what you claim you tried is meaningless, because it uses undefined variables, etc.

What is wrong with norm(V)?

And if that does not work, then what is wrong with sqrt(sum(V.^2))?

If you say you had problems, then you need to say WHAT problems, because what I've written does what you are asking. AND, you need to show code that actually does what you claim you tried.

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