CODEWITHSUNDEEP
pythonsympy
Hooked
Hooked

Reputation: 88198

Coefficients should be Integers: sympy diophantine equations

I have a polynomial (generated from the characteristic polynomial of a matrix) and I'd like to solve for the integer solutions

import sympy
from sympy.solvers.diophantine import diop_linear

M = sympy.Matrix([[0,1,1],[1,0,1],[1,1,0]])
p = M.charpoly()

This polynomial clearly factors into integer roots:

print p.factor()
# (_lambda - 2)*(_lambda + 1)**2

The input polynomial however, is expected to be an integer coefficient type when using diop_linear(p). I'm not sure how to do this using sympy 0.75, despite looking through the docs. The traceback is:

Traceback (most recent call last):
  File "test.py", line 8, in <module>
    diop_linear(p)
  File "/usr/local/lib/python2.7/dist-packages/sympy/solvers/diophantine.py", line 365, in diop_linear
    var, coeff, diop_type = classify_diop(eq)
  File "/usr/local/lib/python2.7/dist-packages/sympy/solvers/diophantine.py", line 232, in classify_diop
    raise TypeError("Coefficients should be Integers")
TypeError: Coefficients should be Integers

Upvotes: 2

Views: 983

Answers (1)

asmeurer
asmeurer

Reputation: 91580

That error message is clearly incorrect. The problem is that diop_linear only works for linear diophantine equations (which for single variable equations are not that interesting). If you just want to solve a single variable equation, just use solve.

Upvotes: 1

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