matlab does not simplify the expression?

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PAOLA
PAOLA 2012-9-29
评论： Luan Trinh 2014-11-27
Hi Everyone,
I would like to find the code to convert the expression (x^10)^1/5 into x^2 but I can't find it. I'm actually trying to come up with an algorithm to solve the SVD. But when trying to find the eigenvectors i have to solve a system of equations with infinite solutions and that's where I get stuck. X1 is defined as follows
X1 =
x1
x2
and I would like to execute
ecua1=X(1); L=sqrt(X1(1)^2 + (solve(ecua1,'x2'))^2)
but in the last line
L=sqrt(X1(1)^2 + (solve(ecua1,'x2'))^2) ---> L = 2^(1/2)*(x1^2)^(1/2)
matlab does not simplify the expression and thus I can't continue.
Please, I would really appreciate any help!!
Thanks,
Paola

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回答（3 个）

Matt Fig
Matt Fig 2012-9-29
编辑：Matt Fig 2012-9-29
syms x
simplify((x^10)^(1/5),'IgnoreAnalyticConstraints',true)
  2 个评论
PAOLA
PAOLA 2012-10-1
Thank you very much for your answer, I tried to use the 'IgnoreAnalyticConstraints' but Mathlab shows the following error ??? Error using ==> sym.simplify Too many input arguments. Do you know if there is any constraint on the use of simplify function on Matlab R2009b 64 bits??
Walter Roberson
Walter Roberson 2012-10-1
R2009b had only very simple constraint management when you call simplify() from the MATLAB level instead of from within MuPAD itself. See the sym() command for how to constrain x to be real-valued.

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Walter Roberson
Walter Roberson 2012-9-29
(x^10)^(1/5) is not generally x^2. p^(1/5) has five complex roots, so (x^10)^(1/5) needs to have 5 solutions, but x^2 is only a single value.
In order to get the simplification you have in mind, you will need to add assumptions of real-valued and non-negative.
  1 个评论
Luan Trinh
Luan Trinh 2014-11-27
Could you help me simplify this function?
syms a si f(si) = (a^2*(51056921947406336*exp(-si*2*i) + 51056921947406336*exp(si*2*i) + 12827342454285926*exp(-si*4*i) + 12827342454285926*exp(si*4*i) + 3572093376318669*exp(-si*6*i) + 3572093376318669*exp(si*6*i) + 301903902754734080)^2)/48357032784585166988247040000000000 ;
Thank you so much.

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PAOLA
PAOLA 2012-10-10
I solve it removing the sym vars. and tried like a polynomial .Thanks for the answers!

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