> > Second Variant (using Poly) kind of works, but there is a small fix
> > required. "mypoly.coeffs" ommits the zeros, therefore if the
> > coefficients for x^0, x^1 and x^3 are 0, they would not appear. Is
> > this a bug or a feature?
[cut]
> Now there must be a better way to do this [...to get the coefficients of a
> polynomial]
In interactive mode, if you do
>>> help(mypoly)
you will receive the documentation about polynomials included in
sympy. If you browse through that you will see there is a method
called .iter_all_coeffs() and that is the one that you want to get ALL
the coefficients, even the zeros:
>>> list(mymonic.iter_all_coeffs())
[1, 2.32000000000000, -126.654400000000, 0, 118.147448015123, 0, 0]
Right now, if you try to pass this directly to polyroots it will
complain because you are sending sympy numbers, but if you change them
all to floats first it works. Here it is step by step:
When you use the iter_all_coeffs() method, you get a generator...
>>> mymonic.iter_all_coeffs()
<generator object iter_all_coeffs at 0x01FF3968>
but polyroots needs a real list of numbers not the thing that can
*make* the list so...
>>> list(_)
[1, 2.32000000000000, -126.654400000000, 0, 118.147448015123, 0, 0]
Now, if you *copied* and pasted those numbers they would work, but if
you tried polyroots(list(mymonic.iter_all_coeffs())) it would fail
because then you are sending the *sympy numbers* directly and right
now polyroots is not ready to handle that. The solution is to turn
them into floating point numbers first:
>>> [float(tmp) for tmp in mo.iter_all_coeffs()]
[1.0, 2.3199999999999998, -126.6544, 0.0, 118.147448015123, 0.0, 0.0]
Putting it all together gives...
>>> mpmath.polyroots([float(tmp) for tmp in mymonic.iter_all_coeffs()])
[mpf('-12.439917313666234'), mpf('-0.96089172423224767'), mpf
('-9.5259289164838849e-19'), mpf('5.8873478448024993e-19'), mpf
('0.97837756504691176'), mpf('10.102431472851569')]
/c
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