ENH: Cast non-object arrays to float in np.poly

Closes #5096. Casts integer arrays to np.double, to prevent
integer overflow. Object arrays are left unchanged, to allow
use of arbitrary precision objects.

1 files changed, 12 insertions, 6 deletions

diff --git a/numpy/lib/polynomial.py b/numpy/lib/polynomial.py
index 7e4ec1485..2b867e244 100644
--- a/numpy/lib/polynomial.py
+++ b/numpy/lib/polynomial.py
@@ -12,10 +12,11 @@ import re
 import warnings
 import numpy.core.numeric as NX
 
-from numpy.core import isscalar, abs, finfo, atleast_1d, hstack, dot
+from numpy.core import (isscalar, abs, finfo, atleast_1d, hstack, dot, array,
+                        ones)
 from numpy.lib.twodim_base import diag, vander
 from numpy.lib.function_base import trim_zeros, sort_complex
-from numpy.lib.type_check import iscomplex, real, imag
+from numpy.lib.type_check import iscomplex, real, imag, mintypecode
 from numpy.linalg import eigvals, lstsq, inv
 
 class RankWarning(UserWarning):
@@ -122,19 +123,24 @@ def poly(seq_of_zeros):
     """
     seq_of_zeros = atleast_1d(seq_of_zeros)
     sh = seq_of_zeros.shape
+
     if len(sh) == 2 and sh[0] == sh[1] and sh[0] != 0:
         seq_of_zeros = eigvals(seq_of_zeros)
     elif len(sh) == 1:
-        pass
+        dt = seq_of_zeros.dtype
+        # Let object arrays slip through, e.g. for arbitrary precision
+        if dt != object:
+            seq_of_zeros = seq_of_zeros.astype(mintypecode(dt.char))
     else:
         raise ValueError("input must be 1d or non-empty square 2d array.")
 
     if len(seq_of_zeros) == 0:
         return 1.0
-
-    a = [1]
+    dt = seq_of_zeros.dtype
+    a = ones((1,), dtype=dt)
     for k in range(len(seq_of_zeros)):
-        a = NX.convolve(a, [1, -seq_of_zeros[k]], mode='full')
+        a = NX.convolve(a, array([1, -seq_of_zeros[k]], dtype=dt),
+                        mode='full')
 
     if issubclass(a.dtype.type, NX.complexfloating):
         # if complex roots are all complex conjugates, the roots are real.