def dup_mul(f, g, K):
"""
Multiply dense polynomials in ``K[x]``.
Examples
========
>>> from sympy.polys import ring, ZZ
>>> R, x = ring("x", ZZ)
>>> R.dup_mul(x - 2, x + 2)
x**2 - 4
"""
if f == g:
return dup_sqr(f, K)
if not (f and g):
return []
df = dup_degree(f)
dg = dup_degree(g)
n = max(df, dg) + 1
if n < 100:
h = []
for i in xrange(0, df + dg + 1):
coeff = K.zero
for j in xrange(max(0, i - dg), min(df, i) + 1):
coeff += f[j]*g[i - j]
h.append(coeff)
return dup_strip(h)
else:
# Use Karatsuba's algorithm (divide and conquer), see e.g.:
# Joris van der Hoeven, Relax But Don't Be Too Lazy,
# J. Symbolic Computation, 11 (2002), section 3.1.1.
n2 = n//2
fl, gl = dup_slice(f, 0, n2, K), dup_slice(g, 0, n2, K)
fh = dup_rshift(dup_slice(f, n2, n, K), n2, K)
gh = dup_rshift(dup_slice(g, n2, n, K), n2, K)
lo, hi = dup_mul(fl, gl, K), dup_mul(fh, gh, K)
mid = dup_mul(dup_add(fl, fh, K), dup_add(gl, gh, K), K)
mid = dup_sub(mid, dup_add(lo, hi, K), K)
return dup_add(dup_add(lo, dup_lshift(mid, n2, K), K),
dup_lshift(hi, 2*n2, K), K)
def dup_mul(f, g, K):
"""
Multiply dense polynomials in ``K[x]``.
Examples
========
>>> from sympy.polys import ring, ZZ
>>> R, x = ring("x", ZZ)
>>> R.dup_mul(x - 2, x + 2)
x**2 - 4
"""
if f == g:
return dup_sqr(f, K)
if not (f and g):
return []
df = dup_degree(f)
dg = dup_degree(g)
n = max(df, dg) + 1
if n < 100:
h = []
for i in range(0, df + dg + 1):
coeff = K.zero
for j in range(max(0, i - dg), min(df, i) + 1):
coeff += f[j] * g[i - j]
h.append(coeff)
return dup_strip(h)
else:
# Use Karatsuba's algorithm (divide and conquer), see e.g.:
# Joris van der Hoeven, Relax But Don't Be Too Lazy,
# J. Symbolic Computation, 11 (2002), section 3.1.1.
n2 = n // 2
fl, gl = dup_slice(f, 0, n2, K), dup_slice(g, 0, n2, K)
fh = dup_rshift(dup_slice(f, n2, n, K), n2, K)
gh = dup_rshift(dup_slice(g, n2, n, K), n2, K)
lo, hi = dup_mul(fl, gl, K), dup_mul(fh, gh, K)
mid = dup_mul(dup_add(fl, fh, K), dup_add(gl, gh, K), K)
mid = dup_sub(mid, dup_add(lo, hi, K), K)
return dup_add(dup_add(lo, dup_lshift(mid, n2, K), K),
dup_lshift(hi, 2 * n2, K), K)
def test_dup_slice():
f = [1, 2, 3, 4]
assert dup_slice(f, 0, 0, ZZ) == []
assert dup_slice(f, 0, 1, ZZ) == [4]
assert dup_slice(f, 0, 2, ZZ) == [3,4]
assert dup_slice(f, 0, 3, ZZ) == [2,3,4]
assert dup_slice(f, 0, 4, ZZ) == [1,2,3,4]
assert dup_slice(f, 0, 4, ZZ) == f
assert dup_slice(f, 0, 9, ZZ) == f
assert dup_slice(f, 1, 0, ZZ) == []
assert dup_slice(f, 1, 1, ZZ) == []
assert dup_slice(f, 1, 2, ZZ) == [3,0]
assert dup_slice(f, 1, 3, ZZ) == [2,3,0]
assert dup_slice(f, 1, 4, ZZ) == [1,2,3,0]