Can vpasolve restrict the numerical solution to be a real number? If it can, how should I stipulate this condition?

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jessie sun 2022-4-24

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评论： jessie sun 2022-4-25

I have eight unknown variables and eight equations. Now I use the vpasolve to find the numerical solution of the equation, hoping to get only the real solution, but the vpasolve only returns a complex solution. Can I restrict the it to output only real solutions? If I can, how should I implement it? Thank you for your reply.

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Answer 1

Dyuman Joshi 2022-4-24

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在 MATLAB Online 中打开

Taken from vpasolve documentation

syms x

S = vpasolve(x^6 - x^2 == 3, x)

S =

assume(x,'real')

S = vpasolve(x^6 - x^2 == 3, [-Inf Inf])

S =

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Answer 2

jessie sun 2022-4-25

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Dear @Dyuman Joshi, I used "assume" to restrict the unknown variables to be real numbers:

But the output result was not as I expected:

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Walter Roberson 2022-4-25

https://www.mathworks.com/help/symbolic/sym.vpasolve.html#bt5205t-5

Tips:

vpasolve ignores assumptions set on variables. You can restrict the returned results to particular ranges by specifying appropriate search ranges using the argument init_param.

jessie sun 2022-4-25