Exact value of a result

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Marc-Samuel
Marc-Samuel 2022-11-29
回答： Walter Roberson 2022-11-29
Hello, I am trying to get the exact values of the following lines :
b=[-1, 3];
a=[1, -3, -2];
[r,p,k]=residuez(b,a);
right now, I obtain something like : p=[3.5615;-0.5615] and r=[-0.1361;-0.8638] and k=1.
Is there a format that would allow me to get me to see it displayed like : p=[(3-sqrt(17))/2 ; (3+sqrt(17))/2] and same for r?
thanks

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回答（2 个）

David Hill
David Hill 2022-11-29
Ran in:
residuez requires doubles as input, but p is just the roots of polynomial a which you could use symbolic to produce.
a=sym([1, -3, -2]);
p=roots(a)
p = 
Walter Roberson
Walter Roberson 2022-11-29
No, the calculations are inherently carried out in floating point.
If you were to follow along in the source code you could strip out the checks for floating point, and you could convert the numeric roots() call to use poly2sym() and then solve for symbolic roots. But after that the code uses filter() to run an impulse through, and emulating that symbolically might take a bit of work.

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