def test_octave_piecewise():
expr = Piecewise((x, x < 1), (x**2, True))
assert mcode(expr) == "((x < 1).*(x) + (~(x < 1)).*(x.^2))"
assert mcode(expr,
assign_to="r") == ("r = ((x < 1).*(x) + (~(x < 1)).*(x.^2));")
assert mcode(expr, assign_to="r", inline=False) == ("if (x < 1)\n"
" r = x;\n"
"else\n"
" r = x.^2;\n"
"end")
expr = Piecewise((x**2, x < 1), (x**3, x < 2), (x**4, x < 3), (x**5, True))
expected = ("((x < 1).*(x.^2) + (~(x < 1)).*( ...\n"
"(x < 2).*(x.^3) + (~(x < 2)).*( ...\n"
"(x < 3).*(x.^4) + (~(x < 3)).*(x.^5))))")
assert mcode(expr) == expected
assert mcode(expr, assign_to="r") == "r = " + expected + ";"
assert mcode(expr, assign_to="r", inline=False) == ("if (x < 1)\n"
" r = x.^2;\n"
"elseif (x < 2)\n"
" r = x.^3;\n"
"elseif (x < 3)\n"
" r = x.^4;\n"
"else\n"
" r = x.^5;\n"
"end")
# Check that Piecewise without a True (default) condition error
expr = Piecewise((x, x < 1), (x**2, x > 1), (sin(x), x > 0))
pytest.raises(ValueError, lambda: mcode(expr))
def test_ccode_Piecewise_deep():
p = ccode(2 * Piecewise((x, x < 1), (x + 1, x < 2), (x**2, True)))
assert p == ("2*((x < 1) ? (\n"
" x\n"
")\n"
": ((x < 2) ? (\n"
" x + 1\n"
")\n"
": (\n"
" pow(x, 2)\n"
")))")
expr = x * y * z + x**2 + y**2 + Piecewise((0, x < 0.5),
(1, True)) + cos(z) - 1
assert ccode(expr) == ("pow(x, 2) + x*y*z + pow(y, 2) + ((x < 0.5) ? (\n"
" 0\n"
")\n"
": (\n"
" 1\n"
")) + cos(z) - 1")
assert ccode(expr, assign_to='c') == (
"c = pow(x, 2) + x*y*z + pow(y, 2) + ((x < 0.5) ? (\n"
" 0\n"
")\n"
": (\n"
" 1\n"
")) + cos(z) - 1;")
def test_deltaproduct_mul_add_x_kd_add_y_kd():
assert dp((x + KD(i, k))*(y + KD(i, j)), (j, 1, 3)) == \
KD(i, 1)*(KD(i, k) + x)*((KD(i, k) + x)*y)**2 + \
KD(i, 2)*(KD(i, k) + x)*y*(KD(i, k) + x)**2*y + \
KD(i, 3)*((KD(i, k) + x)*y)**2*(KD(i, k) + x) + \
((KD(i, k) + x)*y)**3
assert dp((x + KD(i, k))*(y + KD(i, j)), (j, 1, 1)) == \
(x + KD(i, k))*(y + KD(i, 1))
assert dp((x + KD(i, k))*(y + KD(i, j)), (j, 2, 2)) == \
(x + KD(i, k))*(y + KD(i, 2))
assert dp((x + KD(i, k))*(y + KD(i, j)), (j, 3, 3)) == \
(x + KD(i, k))*(y + KD(i, 3))
assert dp((x + KD(i, k))*(y + KD(i, j)), (j, 1, k)) == \
((x + KD(i, k))*y)**k + Piecewise(
(((x + KD(i, k))*y)**(i - 1)*(x + KD(i, k)) *
((x + KD(i, k))*y)**(-i + k), And(Integer(1) <= i, i <= k)),
(0, True)
)
assert dp((x + KD(i, k))*(y + KD(i, j)), (j, k, 3)) == \
((x + KD(i, k))*y)**(4 - k) + Piecewise(
(((x + KD(i, k))*y)**(i - k)*(x + KD(i, k)) *
((x + KD(i, k))*y)**(-i + 3), And(k <= i, i <= 3)),
(0, True)
)
assert dp((x + KD(i, k))*(y + KD(i, j)), (j, k, l)) == \
((x + KD(i, k))*y)**(-k + l + 1) + Piecewise(
(((x + KD(i, k))*y)**(i - k)*(x + KD(i, k)) *
((x + KD(i, k))*y)**(-i + l), And(k <= i, i <= l)),
(0, True)
)
def test_deltaproduct_mul_add_x_y_add_y_kd():
assert dp((x + y)*(y + KD(i, j)), (j, 1, 3)) == ((x + y)*y)**3 + \
(x + y)*((x + y)*y)**2*KD(i, 1) + \
(x + y)*y*(x + y)**2*y*KD(i, 2) + \
((x + y)*y)**2*(x + y)*KD(i, 3)
assert dp((x + y) * (y + KD(i, j)), (j, 1, 1)) == (x + y) * (y + KD(i, 1))
assert dp((x + y) * (y + KD(i, j)), (j, 2, 2)) == (x + y) * (y + KD(i, 2))
assert dp((x + y) * (y + KD(i, j)), (j, 3, 3)) == (x + y) * (y + KD(i, 3))
assert dp((x + y)*(y + KD(i, j)), (j, 1, k)) == \
((x + y)*y)**k + Piecewise(
(((x + y)*y)**(i - 1)*(x + y)*((x + y)*y)**(k - i),
And(Integer(1) <= i, i <= k)),
(0, True)
)
assert dp((x + y)*(y + KD(i, j)), (j, k, 3)) == \
((x + y)*y)**(-k + 4) + Piecewise(
(((x + y)*y)**(i - k)*(x + y)*((x + y)*y)**(3 - i),
And(k <= i, i <= 3)),
(0, True)
)
assert dp((x + y)*(y + KD(i, j)), (j, k, l)) == \
((x + y)*y)**(-k + l + 1) + Piecewise(
(((x + y)*y)**(i - k)*(x + y)*((x + y)*y)**(l - i),
And(k <= i, i <= l)),
(0, True)
)
def try_meijerg(function, xab):
ret = None
if len(xab) == 3 and meijerg is not False:
x, a, b = xab
try:
res = meijerint_definite(function, x, a, b)
except NotImplementedError:
from diofant.integrals.meijerint import _debug
_debug('NotImplementedError from meijerint_definite')
res = None
if res is not None:
f, cond = res
if conds == 'piecewise':
ret = Piecewise((f, cond),
(self.func(function,
(x, a, b)), True))
elif conds == 'separate':
if len(self.limits) != 1:
raise ValueError(
'conds=separate not supported in '
'multiple integrals')
ret = f, cond
else:
ret = f
return ret
def _eval_rewrite_as_Sum(self, ap, bq, z):
from diofant.functions import factorial, RisingFactorial, Piecewise
from diofant import Sum
n = Dummy("n", integer=True)
rfap = Tuple(*[RisingFactorial(a, n) for a in ap])
rfbq = Tuple(*[RisingFactorial(b, n) for b in bq])
coeff = Mul(*rfap) / Mul(*rfbq)
return Piecewise((Sum(coeff * z**n / factorial(n),
(n, 0, oo)), self.convergence_statement),
(self, True))
def test_trigintegrate_odd():
assert trigintegrate(Rational(1), x) == x
assert trigintegrate(x, x) is None
assert trigintegrate(x**2, x) is None
assert trigintegrate(sin(x), x) == -cos(x)
assert trigintegrate(cos(x), x) == sin(x)
assert trigintegrate(sin(3 * x), x) == -cos(3 * x) / 3
assert trigintegrate(cos(3 * x), x) == sin(3 * x) / 3
y = Symbol('y')
assert trigintegrate(sin(y*x), x) == \
Piecewise((0, Eq(y, 0)), (-cos(y*x)/y, True))
assert trigintegrate(cos(y*x), x) == \
Piecewise((x, Eq(y, 0)), (sin(y*x)/y, True))
assert trigintegrate(sin(y*x)**2, x) == \
Piecewise((0, Eq(y, 0)), ((x*y/2 - sin(x*y)*cos(x*y)/2)/y, True))
assert trigintegrate(sin(y*x)*cos(y*x), x) == \
Piecewise((0, Eq(y, 0)), (sin(x*y)**2/(2*y), True))
assert trigintegrate(cos(y*x)**2, x) == \
Piecewise((x, Eq(y, 0)), ((x*y/2 + sin(x*y)*cos(x*y)/2)/y, True))
y = Symbol('y', positive=True)
# TODO: remove conds='none' below. For this to work we would have to rule
# out (e.g. by trying solve) the condition y = 0, incompatible with
# y.is_positive being True.
assert trigintegrate(sin(y * x), x, conds='none') == -cos(y * x) / y
assert trigintegrate(cos(y * x), x, conds='none') == sin(y * x) / y
assert trigintegrate(sin(x) * cos(x), x) == sin(x)**2 / 2
assert trigintegrate(sin(x) * cos(x)**2, x) == -cos(x)**3 / 3
assert trigintegrate(sin(x)**2 * cos(x), x) == sin(x)**3 / 3
# check if it selects right function to substitute,
# so the result is kept simple
assert trigintegrate(sin(x)**7 * cos(x), x) == sin(x)**8 / 8
assert trigintegrate(sin(x) * cos(x)**7, x) == -cos(x)**8 / 8
assert trigintegrate(sin(x)**7 * cos(x)**3, x) == \
-sin(x)**10/10 + sin(x)**8/8
assert trigintegrate(sin(x)**3 * cos(x)**7, x) == \
cos(x)**10/10 - cos(x)**8/8
def _add_splines(c, b1, d, b2):
"""Construct c*b1 + d*b2."""
if b1 == S.Zero or c == S.Zero:
rv = piecewise_fold(d * b2)
elif b2 == S.Zero or d == S.Zero:
rv = piecewise_fold(c * b1)
else:
new_args = []
n_intervals = len(b1.args)
if n_intervals != len(b2.args):
raise ValueError("Args of b1 and b2 are not equal")
new_args.append((c * b1.args[0].expr, b1.args[0].cond))
for i in range(1, n_intervals - 1):
new_args.append((c * b1.args[i].expr + d * b2.args[i - 1].expr,
b1.args[i].cond))
new_args.append((d * b2.args[-2].expr, b2.args[-2].cond))
new_args.append(b2.args[-1])
rv = Piecewise(*new_args)
return rv.expand()
def test_jscode_Piecewise_deep():
p = jscode(2*Piecewise((x, x < 1), (x**2, True)))
s = \
"""\
2*((x < 1) ? (
x
)
: (
Math.pow(x, 2)
))\
"""
assert p == s
def test_deltaproduct_mul_x_add_y_twokd():
assert dp(x*(y + 2*KD(i, j)), (j, 1, 3)) == (x*y)**3 + \
2*x*(x*y)**2*KD(i, 1) + 2*x*y*x*x*y*KD(i, 2) + 2*(x*y)**2*x*KD(i, 3)
assert dp(x * (y + 2 * KD(i, j)), (j, 1, 1)) == x * (y + 2 * KD(i, 1))
assert dp(x * (y + 2 * KD(i, j)), (j, 2, 2)) == x * (y + 2 * KD(i, 2))
assert dp(x * (y + 2 * KD(i, j)), (j, 3, 3)) == x * (y + 2 * KD(i, 3))
assert dp(x*(y + 2*KD(i, j)), (j, 1, k)) == \
(x*y)**k + Piecewise(
(2*(x*y)**(i - 1)*x*(x*y)**(k - i), And(Integer(1) <= i, i <= k)),
(0, True)
)
assert dp(x*(y + 2*KD(i, j)), (j, k, 3)) == \
(x*y)**(-k + 4) + Piecewise(
(2*(x*y)**(i - k)*x*(x*y)**(3 - i), And(k <= i, i <= 3)),
(0, True)
)
assert dp(x*(y + 2*KD(i, j)), (j, k, l)) == \
(x*y)**(-k + l + 1) + Piecewise(
(2*(x*y)**(i - k)*x*(x*y)**(l - i), And(k <= i, i <= l)),
(0, True)
)
def test_trick_indent_with_end_else_words():
# words starting with "end" or "else" do not confuse the indenter
t1 = sympify('endless')
t2 = sympify('elsewhere')
pw = Piecewise((t1, x < 0), (t2, x <= 1), (1, True))
assert mcode(pw, inline=False) == ("if (x < 0)\n"
" endless\n"
"elseif (x <= 1)\n"
" elsewhere\n"
"else\n"
" 1\n"
"end")
def test_deltasummation_basic_numerical():
n = symbols('n', integer=True, nonzero=True)
assert ds(KD(n, 0), (n, 1, 3)) == 0
# return unevaluated, until it gets implemented
assert ds(KD(i**2, j**2), (j, -oo, oo)) == \
Sum(KD(i**2, j**2), (j, -oo, oo))
assert Piecewise((KD(i, k), And(Integer(1) <= i, i <= 3)), (0, True)) == \
ds(KD(i, j)*KD(j, k), (j, 1, 3)) == \
ds(KD(j, k)*KD(i, j), (j, 1, 3))
assert ds(KD(i, k), (k, -oo, oo)) == 1
assert ds(KD(i, k), (k, 0, oo)) == Piecewise((1, Integer(0) <= i),
(0, True))
assert ds(KD(i, k), (k, 1, 3)) == \
Piecewise((1, And(Integer(1) <= i, i <= 3)), (0, True))
assert ds(k * KD(i, j) * KD(j, k), (k, -oo, oo)) == j * KD(i, j)
assert ds(j * KD(i, j), (j, -oo, oo)) == i
assert ds(i * KD(i, j), (i, -oo, oo)) == j
assert ds(x, (i, 1, 3)) == 3 * x
assert ds((i + j) * KD(i, j), (j, -oo, oo)) == 2 * i
def test_Matrix_printing():
# Test returning a Matrix
mat = Matrix([x*y, Piecewise((2 + x, y > 0), (y, True)), sin(z)])
A = MatrixSymbol('A', 3, 1)
assert jscode(mat, A) == (
"A[0] = x*y;\n"
"if (y > 0) {\n"
" A[1] = x + 2;\n"
"}\n"
"else {\n"
" A[1] = y;\n"
"}\n"
"A[2] = Math.sin(z);")
# Test using MatrixElements in expressions
expr = Piecewise((2*A[2, 0], x > 0), (A[2, 0], True)) + sin(A[1, 0]) + A[0, 0]
assert jscode(expr) == (
"((x > 0) ? (\n"
" 2*A[2]\n"
")\n"
": (\n"
" A[2]\n"
")) + Math.sin(A[1]) + A[0]")
# Test using MatrixElements in a Matrix
q = MatrixSymbol('q', 5, 1)
M = MatrixSymbol('M', 3, 3)
m = Matrix([[sin(q[1, 0]), 0, cos(q[2, 0])],
[q[1, 0] + q[2, 0], q[3, 0], 5],
[2*q[4, 0]/q[1, 0], sqrt(q[0, 0]) + 4, 0]])
assert jscode(m, M) == (
"M[0] = Math.sin(q[1]);\n"
"M[1] = 0;\n"
"M[2] = Math.cos(q[2]);\n"
"M[3] = q[1] + q[2];\n"
"M[4] = q[3];\n"
"M[5] = 5;\n"
"M[6] = 2*q[4]*1/q[1];\n"
"M[7] = 4 + Math.sqrt(q[0]);\n"
"M[8] = 0;")
def test_deltasummation_mul_x_kd():
assert ds(x*KD(i, j), (j, 1, 3)) == \
Piecewise((x, And(Integer(1) <= i, i <= 3)), (0, True))
assert ds(x * KD(i, j), (j, 1, 1)) == Piecewise((x, Eq(i, 1)), (0, True))
assert ds(x * KD(i, j), (j, 2, 2)) == Piecewise((x, Eq(i, 2)), (0, True))
assert ds(x * KD(i, j), (j, 3, 3)) == Piecewise((x, Eq(i, 3)), (0, True))
assert ds(x*KD(i, j), (j, 1, k)) == \
Piecewise((x, And(Integer(1) <= i, i <= k)), (0, True))
assert ds(x*KD(i, j), (j, k, 3)) == \
Piecewise((x, And(k <= i, i <= 3)), (0, True))
assert ds(x*KD(i, j), (j, k, l)) == \
Piecewise((x, And(k <= i, i <= l)), (0, True))
def test_deltasummation_basic_symbolic():
assert ds(KD(i, j), (j, 1, 3)) == \
Piecewise((1, And(Integer(1) <= i, i <= 3)), (0, True))
assert ds(KD(i, j), (j, 1, 1)) == Piecewise((1, Eq(i, 1)), (0, True))
assert ds(KD(i, j), (j, 2, 2)) == Piecewise((1, Eq(i, 2)), (0, True))
assert ds(KD(i, j), (j, 3, 3)) == Piecewise((1, Eq(i, 3)), (0, True))
assert ds(KD(i, j), (j, 1, k)) == \
Piecewise((1, And(Integer(1) <= i, i <= k)), (0, True))
assert ds(KD(i, j), (j, k, 3)) == \
Piecewise((1, And(k <= i, i <= 3)), (0, True))
assert ds(KD(i, j), (j, k, l)) == \
Piecewise((1, And(k <= i, i <= l)), (0, True))
def test_jscode_Piecewise():
expr = Piecewise((x, x < 1), (x**2, True))
p = jscode(expr)
s = \
"""\
((x < 1) ? (
x
)
: (
Math.pow(x, 2)
))\
"""
assert p == s
assert jscode(expr, assign_to="c") == (
"if (x < 1) {\n"
" c = x;\n"
"}\n"
"else {\n"
" c = Math.pow(x, 2);\n"
"}")
# Check that Piecewise without a True (default) condition error
expr = Piecewise((x, x < 1), (x**2, x > 1), (sin(x), x > 0))
pytest.raises(ValueError, lambda: jscode(expr))
def test_ccode_Piecewise():
expr = Piecewise((x, x < 1), (x**2, True))
assert ccode(expr) == ("((x < 1) ? (\n"
" x\n"
")\n"
": (\n"
" pow(x, 2)\n"
"))")
assert ccode(expr, assign_to="c") == ("if (x < 1) {\n"
" c = x;\n"
"}\n"
"else {\n"
" c = pow(x, 2);\n"
"}")
expr = Piecewise((x, x < 1), (x + 1, x < 2), (x**2, True))
assert ccode(expr) == ("((x < 1) ? (\n"
" x\n"
")\n"
": ((x < 2) ? (\n"
" x + 1\n"
")\n"
": (\n"
" pow(x, 2)\n"
")))")
assert ccode(expr, assign_to='c') == ("if (x < 1) {\n"
" c = x;\n"
"}\n"
"else if (x < 2) {\n"
" c = x + 1;\n"
"}\n"
"else {\n"
" c = pow(x, 2);\n"
"}")
# Check that Piecewise without a True (default) condition error
expr = Piecewise((x, x < 1), (x**2, x > 1), (sin(x), x > 0))
pytest.raises(ValueError, lambda: ccode(expr))
def test_deltasummation_mul_x_add_y_kd():
assert ds(x*(y + KD(i, j)), (j, 1, 3)) == \
Piecewise((3*x*y + x, And(Integer(1) <= i, i <= 3)), (3*x*y, True))
assert ds(x*(y + KD(i, j)), (j, 1, 1)) == \
Piecewise((x*y + x, Eq(i, 1)), (x*y, True))
assert ds(x*(y + KD(i, j)), (j, 2, 2)) == \
Piecewise((x*y + x, Eq(i, 2)), (x*y, True))
assert ds(x*(y + KD(i, j)), (j, 3, 3)) == \
Piecewise((x*y + x, Eq(i, 3)), (x*y, True))
assert ds(x*(y + KD(i, j)), (j, 1, k)) == \
Piecewise((k*x*y + x, And(Integer(1) <= i, i <= k)), (k*x*y, True))
assert ds(x*(y + KD(i, j)), (j, k, 3)) == \
Piecewise(((4 - k)*x*y + x, And(k <= i, i <= 3)), ((4 - k)*x*y, True))
assert ds(x * (y + KD(i, j)), (j, k, l)) == Piecewise(
((l - k + 1) * x * y + x, And(k <= i, i <= l)),
((l - k + 1) * x * y, True))
def _eval_rewrite_as_nonrep(self, *args):
from diofant import Piecewise
x, n = self.args[-1].extract_branch_factor(allow_half=True)
minus = False
newargs = self.args[:-1] + (x, )
if not n.is_Integer:
minus = True
n -= Rational(1, 2)
newerargs = newargs + (n, )
if minus:
small = self._expr_small_minus(*newargs)
big = self._expr_big_minus(*newerargs)
else:
small = self._expr_small(*newargs)
big = self._expr_big(*newerargs)
if big == small:
return small
return Piecewise((big, abs(x) > 1), (small, True))
def test_deltasummation_mul_add_x_kd_add_y_kd():
assert ds((x + KD(i, k)) * (y + KD(i, j)), (j, 1, 3)) == piecewise_fold(
Piecewise((KD(i, k) + x, And(Integer(1) <= i, i <= 3)), (0, True)) +
3 * (KD(i, k) + x) * y)
assert ds((x + KD(i, k)) * (y + KD(i, j)), (j, 1, 1)) == piecewise_fold(
Piecewise((KD(i, k) + x, Eq(i, 1)), (0, True)) + (KD(i, k) + x) * y)
assert ds((x + KD(i, k)) * (y + KD(i, j)), (j, 2, 2)) == piecewise_fold(
Piecewise((KD(i, k) + x, Eq(i, 2)), (0, True)) + (KD(i, k) + x) * y)
assert ds((x + KD(i, k)) * (y + KD(i, j)), (j, 3, 3)) == piecewise_fold(
Piecewise((KD(i, k) + x, Eq(i, 3)), (0, True)) + (KD(i, k) + x) * y)
assert ds((x + KD(i, k)) * (y + KD(i, j)), (j, 1, k)) == piecewise_fold(
Piecewise((KD(i, k) + x, And(Integer(1) <= i, i <= k)), (0, True)) +
k * (KD(i, k) + x) * y)
assert ds((x + KD(i, k)) * (y + KD(i, j)), (j, k, 3)) == piecewise_fold(
Piecewise((KD(i, k) + x, And(k <= i, i <= 3)), (0, True)) + (4 - k) *
(KD(i, k) + x) * y)
assert ds((x + KD(i, k)) * (y + KD(i, j)), (j, k, l)) == piecewise_fold(
Piecewise((KD(i, k) + x, And(k <= i, i <= l)), (0, True)) +
(l - k + 1) * (KD(i, k) + x) * y)
def test_functions():
one_var = (acosh, ln, Heaviside, factorial, bernoulli, coth, tanh, sign,
arg, asin, DiracDelta, re, Abs, sinh, cos, cot, acos, acot,
gamma, bell, harmonic, LambertW, zeta, log, factorial, asinh,
acoth, cosh, dirichlet_eta, loggamma, erf, ceiling, im,
fibonacci, conjugate, tan, floor, atanh, sin, atan, lucas, exp)
two_var = (rf, ff, lowergamma, chebyshevu, chebyshevt, binomial, atan2,
polygamma, hermite, legendre, uppergamma)
others = (chebyshevt_root, chebyshevu_root, Eijk(x, y, z),
Piecewise((0, x < -1), (x**2, x <= 1),
(x**3, True)), assoc_legendre)
for cls in one_var:
check(cls)
c = cls(x)
check(c)
for cls in two_var:
check(cls)
c = cls(x, y)
check(c)
for cls in others:
check(cls)
def _eval_integral(self,
f,
x,
meijerg=None,
risch=None,
conds='piecewise'):
"""
Calculate the anti-derivative to the function f(x).
The following algorithms are applied (roughly in this order):
1. Simple heuristics (based on pattern matching and integral table):
- most frequently used functions (e.g. polynomials, products of trig functions)
2. Integration of rational functions:
- A complete algorithm for integrating rational functions is
implemented (the Lazard-Rioboo-Trager algorithm). The algorithm
also uses the partial fraction decomposition algorithm
implemented in apart() as a preprocessor to make this process
faster. Note that the integral of a rational function is always
elementary, but in general, it may include a RootSum.
3. Full Risch algorithm:
- The Risch algorithm is a complete decision
procedure for integrating elementary functions, which means that
given any elementary function, it will either compute an
elementary antiderivative, or else prove that none exists.
Currently, part of transcendental case is implemented, meaning
elementary integrals containing exponentials, logarithms, and
(soon!) trigonometric functions can be computed. The algebraic
case, e.g., functions containing roots, is much more difficult
and is not implemented yet.
- If the routine fails (because the integrand is not elementary, or
because a case is not implemented yet), it continues on to the
next algorithms below. If the routine proves that the integrals
is nonelementary, it still moves on to the algorithms below,
because we might be able to find a closed-form solution in terms
of special functions. If risch=True, however, it will stop here.
4. The Meijer G-Function algorithm:
- This algorithm works by first rewriting the integrand in terms of
very general Meijer G-Function (meijerg in Diofant), integrating
it, and then rewriting the result back, if possible. This
algorithm is particularly powerful for definite integrals (which
is actually part of a different method of Integral), since it can
compute closed-form solutions of definite integrals even when no
closed-form indefinite integral exists. But it also is capable
of computing many indefinite integrals as well.
- Another advantage of this method is that it can use some results
about the Meijer G-Function to give a result in terms of a
Piecewise expression, which allows to express conditionally
convergent integrals.
- Setting meijerg=True will cause integrate() to use only this
method.
5. The Heuristic Risch algorithm:
- This is a heuristic version of the Risch algorithm, meaning that
it is not deterministic. This is tried as a last resort because
it can be very slow. It is still used because not enough of the
full Risch algorithm is implemented, so that there are still some
integrals that can only be computed using this method. The goal
is to implement enough of the Risch and Meijer G-function methods
so that this can be deleted.
"""
from diofant.integrals.deltafunctions import deltaintegrate
from diofant.integrals.heurisch import heurisch, heurisch_wrapper
from diofant.integrals.rationaltools import ratint
from diofant.integrals.risch import risch_integrate
if risch:
try:
return risch_integrate(f, x, conds=conds)
except NotImplementedError:
return
# if it is a poly(x) then let the polynomial integrate itself (fast)
#
# It is important to make this check first, otherwise the other code
# will return a diofant expression instead of a Polynomial.
#
# see Polynomial for details.
if isinstance(f, Poly) and not meijerg:
return f.integrate(x)
# Piecewise antiderivatives need to call special integrate.
if f.func is Piecewise:
return f._eval_integral(x)
# let's cut it short if `f` does not depend on `x`
if not f.has(x):
return f * x
# try to convert to poly(x) and then integrate if successful (fast)
poly = f.as_poly(x)
if poly is not None and not meijerg:
return poly.integrate().as_expr()
if risch is not False:
try:
result, i = risch_integrate(f,
x,
separate_integral=True,
conds=conds)
except NotImplementedError:
pass
else:
if i:
# There was a nonelementary integral. Try integrating it.
return result + i.doit(risch=False)
else:
return result
# since Integral(f=g1+g2+...) == Integral(g1) + Integral(g2) + ...
# we are going to handle Add terms separately,
# if `f` is not Add -- we only have one term
# Note that in general, this is a bad idea, because Integral(g1) +
# Integral(g2) might not be computable, even if Integral(g1 + g2) is.
# For example, Integral(x**x + x**x*log(x)). But many heuristics only
# work term-wise. So we compute this step last, after trying
# risch_integrate. We also try risch_integrate again in this loop,
# because maybe the integral is a sum of an elementary part and a
# nonelementary part (like erf(x) + exp(x)). risch_integrate() is
# quite fast, so this is acceptable.
parts = []
args = Add.make_args(f)
for g in args:
coeff, g = g.as_independent(x)
# g(x) = const
if g is S.One and not meijerg:
parts.append(coeff * x)
continue
# g(x) = expr + O(x**n)
order_term = g.getO()
if order_term is not None:
h = self._eval_integral(g.removeO(), x)
if h is not None:
parts.append(coeff *
(h + self.func(order_term, *self.limits)))
continue
# NOTE: if there is O(x**n) and we fail to integrate then there is
# no point in trying other methods because they will fail anyway.
return
# c
# g(x) = (a*x+b)
if g.is_Pow and not g.exp.has(x) and not meijerg:
a = Wild('a', exclude=[x])
b = Wild('b', exclude=[x])
M = g.base.match(a * x + b)
if M is not None:
if g.exp == -1:
h = log(g.base)
elif conds != 'piecewise':
h = g.base**(g.exp + 1) / (g.exp + 1)
else:
h1 = log(g.base)
h2 = g.base**(g.exp + 1) / (g.exp + 1)
h = Piecewise((h1, Eq(g.exp, -1)), (h2, True))
parts.append(coeff * h / M[a])
continue
# poly(x)
# g(x) = -------
# poly(x)
if g.is_rational_function(x) and not meijerg:
parts.append(coeff * ratint(g, x))
continue
if not meijerg:
# g(x) = Mul(trig)
h = trigintegrate(g, x, conds=conds)
if h is not None:
parts.append(coeff * h)
continue
# g(x) has at least a DiracDelta term
h = deltaintegrate(g, x)
if h is not None:
parts.append(coeff * h)
continue
# Try risch again.
if risch is not False:
try:
h, i = risch_integrate(g,
x,
separate_integral=True,
conds=conds)
except NotImplementedError:
h = None
else:
if i:
h = h + i.doit(risch=False)
parts.append(coeff * h)
continue
# fall back to heurisch
try:
if conds == 'piecewise':
h = heurisch_wrapper(g, x, hints=[])
else:
h = heurisch(g, x, hints=[])
except PolynomialError:
# XXX: this exception means there is a bug in the
# implementation of heuristic Risch integration
# algorithm.
h = None
else:
h = None
if meijerg is not False and h is None:
# rewrite using G functions
try:
h = meijerint_indefinite(g, x)
except NotImplementedError:
from diofant.integrals.meijerint import _debug
_debug('NotImplementedError from meijerint_definite')
res = None
if h is not None:
parts.append(coeff * h)
continue
# if we failed maybe it was because we had
# a product that could have been expanded,
# so let's try an expansion of the whole
# thing before giving up; we don't try this
# at the outset because there are things
# that cannot be solved unless they are
# NOT expanded e.g., x**x*(1+log(x)). There
# should probably be a checker somewhere in this
# routine to look for such cases and try to do
# collection on the expressions if they are already
# in an expanded form
if not h and len(args) == 1:
f = f.expand(mul=True, deep=False)
if f.is_Add:
# Note: risch will be identical on the expanded
# expression, but maybe it will be able to pick out parts,
# like x*(exp(x) + erf(x)).
return self._eval_integral(f,
x,
meijerg=meijerg,
risch=risch,
conds=conds)
if h is not None:
parts.append(coeff * h)
else:
return
return Add(*parts)
def bspline_basis(d, knots, n, x, close=True):
"""The `n`-th B-spline at `x` of degree `d` with knots.
B-Splines are piecewise polynomials of degree `d` [1]_. They are defined on
a set of knots, which is a sequence of integers or floats.
The 0th degree splines have a value of one on a single interval:
>>> from diofant import bspline_basis
>>> from diofant.abc import x
>>> d = 0
>>> knots = range(5)
>>> bspline_basis(d, knots, 0, x)
Piecewise((1, And(x <= 1, x >= 0)), (0, true))
For a given ``(d, knots)`` there are ``len(knots)-d-1`` B-splines defined, that
are indexed by ``n`` (starting at 0).
Here is an example of a cubic B-spline:
>>> bspline_basis(3, range(5), 0, x)
Piecewise((x**3/6, And(x < 1, x >= 0)),
(-x**3/2 + 2*x**2 - 2*x + 2/3, And(x < 2, x >= 1)),
(x**3/2 - 4*x**2 + 10*x - 22/3, And(x < 3, x >= 2)),
(-x**3/6 + 2*x**2 - 8*x + 32/3, And(x <= 4, x >= 3)),
(0, true))
By repeating knot points, you can introduce discontinuities in the
B-splines and their derivatives:
>>> d = 1
>>> knots = [0,0,2,3,4]
>>> bspline_basis(d, knots, 0, x)
Piecewise((-x/2 + 1, And(x <= 2, x >= 0)), (0, true))
It is quite time consuming to construct and evaluate B-splines. If you
need to evaluate a B-splines many times, it is best to lambdify them
first:
>>> from diofant import lambdify
>>> d = 3
>>> knots = range(10)
>>> b0 = bspline_basis(d, knots, 0, x)
>>> f = lambdify(x, b0)
>>> y = f(0.5)
See Also
========
diofant.functions.special.bsplines.bspline_basis_set
References
==========
.. [1] http://en.wikipedia.org/wiki/B-spline
"""
knots = [sympify(k) for k in knots]
d = int(d)
n = int(n)
n_knots = len(knots)
n_intervals = n_knots - 1
if n + d + 1 > n_intervals:
raise ValueError('n + d + 1 must not exceed len(knots) - 1')
if d == 0:
result = Piecewise(
(S.One, Interval(knots[n], knots[n + 1], False,
not close).contains(x)), (0, True))
elif d > 0:
denom = knots[n + d + 1] - knots[n + 1]
if denom != S.Zero:
B = (knots[n + d + 1] - x) / denom
b2 = bspline_basis(d - 1, knots, n + 1, x, close)
else:
b2 = B = S.Zero
denom = knots[n + d] - knots[n]
if denom != S.Zero:
A = (x - knots[n]) / denom
b1 = bspline_basis(d - 1, knots, n, x, close
and (B == S.Zero or b2 == S.Zero))
else:
b1 = A = S.Zero
result = _add_splines(A, b1, B, b2)
else:
raise ValueError('degree must be non-negative: %r' % n)
return result
def trigintegrate(f, x, conds='piecewise'):
"""Integrate f = Mul(trig) over x
>>> from diofant import Symbol, sin, cos, tan, sec, csc, cot
>>> from diofant.integrals.trigonometry import trigintegrate
>>> from diofant.abc import x
>>> trigintegrate(sin(x)*cos(x), x)
sin(x)**2/2
>>> trigintegrate(sin(x)**2, x)
x/2 - sin(x)*cos(x)/2
>>> trigintegrate(tan(x)*sec(x), x)
1/cos(x)
>>> trigintegrate(sin(x)*tan(x), x)
-log(sin(x) - 1)/2 + log(sin(x) + 1)/2 - sin(x)
http://en.wikibooks.org/wiki/Calculus/Integration_techniques
See Also
========
diofant.integrals.integrals.Integral.doit
diofant.integrals.integrals.Integral
"""
from diofant.integrals.integrals import integrate
pat, a, n, m = _pat_sincos(x)
f = f.rewrite('sincos')
M = f.match(pat)
if M is None:
return
n, m = M[n], M[m]
if n is S.Zero and m is S.Zero:
return x
zz = x if n is S.Zero else S.Zero
a = M[a]
if n.is_odd or m.is_odd:
u = _u
n_, m_ = n.is_odd, m.is_odd
# take smallest n or m -- to choose simplest substitution
if n_ and m_:
n_ = n_ and (n < m) # NB: careful here, one of the
m_ = m_ and not (n < m) # conditions *must* be true
# n m u=C (n-1)/2 m
# S(x) * C(x) dx --> -(1-u^2) * u du
if n_:
ff = -(1 - u**2)**((n - 1) / 2) * u**m
uu = cos(a * x)
# n m u=S n (m-1)/2
# S(x) * C(x) dx --> u * (1-u^2) du
elif m_:
ff = u**n * (1 - u**2)**((m - 1) / 2)
uu = sin(a * x)
fi = integrate(ff, u) # XXX cyclic deps
fx = fi.subs(u, uu)
if conds == 'piecewise':
return Piecewise((zz, Eq(a, 0)), (fx / a, True))
return fx / a
# n & m are both even
#
# 2k 2m 2l 2l
# we transform S (x) * C (x) into terms with only S (x) or C (x)
#
# example:
# 100 4 100 2 2 100 4 2
# S (x) * C (x) = S (x) * (1-S (x)) = S (x) * (1 + S (x) - 2*S (x))
#
# 104 102 100
# = S (x) - 2*S (x) + S (x)
# 2k
# then S is integrated with recursive formula
# take largest n or m -- to choose simplest substitution
n_ = (abs(n) > abs(m))
m_ = (abs(m) > abs(n))
res = S.Zero
if n_:
# 2k 2 k i 2i
# C = (1 - S ) = sum(i, (-) * B(k, i) * S )
if m > 0:
for i in range(0, m // 2 + 1):
res += ((-1)**i * binomial(m // 2, i) *
_sin_pow_integrate(n + 2 * i, x))
elif m == 0:
res = _sin_pow_integrate(n, x)
else:
# m < 0 , |n| > |m|
# /
# |
# | m n
# | cos (x) sin (x) dx =
# |
# |
# /
# /
# |
# -1 m+1 n-1 n - 1 | m+2 n-2
# ________ cos (x) sin (x) + _______ | cos (x) sin (x) dx
# |
# m + 1 m + 1 |
# /
res = (Rational(-1, m + 1) * cos(x)**(m + 1) * sin(x)**(n - 1) +
Rational(n - 1, m + 1) *
trigintegrate(cos(x)**(m + 2) * sin(x)**(n - 2), x))
elif m_:
# 2k 2 k i 2i
# S = (1 - C ) = sum(i, (-) * B(k, i) * C )
if n > 0:
# / /
# | |
# | m n | -m n
# | cos (x)*sin (x) dx or | cos (x) * sin (x) dx
# | |
# / /
#
# |m| > |n| ; m, n >0 ; m, n belong to Z - {0}
# n 2
# sin (x) term is expanded here in terms of cos (x),
# and then integrated.
#
for i in range(0, n // 2 + 1):
res += ((-1)**i * binomial(n // 2, i) *
_cos_pow_integrate(m + 2 * i, x))
elif n == 0:
# /
# |
# | 1
# | _ _ _
# | m
# | cos (x)
# /
#
res = _cos_pow_integrate(m, x)
else:
# n < 0 , |m| > |n|
# /
# |
# | m n
# | cos (x) sin (x) dx =
# |
# |
# /
# /
# |
# 1 m-1 n+1 m - 1 | m-2 n+2
# _______ cos (x) sin (x) + _______ | cos (x) sin (x) dx
# |
# n + 1 n + 1 |
# /
res = (Rational(1, n + 1) * cos(x)**(m - 1) * sin(x)**(n + 1) +
Rational(m - 1, n + 1) *
trigintegrate(cos(x)**(m - 2) * sin(x)**(n + 2), x))
else:
if m == n:
# Substitute sin(2x)/2 for sin(x)cos(x) and then Integrate.
res = integrate((Rational(1, 2) * sin(2 * x))**m, x)
elif (m == -n):
if n < 0:
# Same as the scheme described above.
# the function argument to integrate in the end will
# be 1 , this cannot be integrated by trigintegrate.
# Hence use diofant.integrals.integrate.
res = (Rational(1, n + 1) * cos(x)**(m - 1) * sin(x)**(n + 1) +
Rational(m - 1, n + 1) *
integrate(cos(x)**(m - 2) * sin(x)**(n + 2), x))
else:
res = (
Rational(-1, m + 1) * cos(x)**(m + 1) * sin(x)**(n - 1) +
Rational(n - 1, m + 1) *
integrate(cos(x)**(m + 2) * sin(x)**(n - 2), x))
if conds == 'piecewise':
return Piecewise((zz, Eq(a, 0)), (res.subs(x, a * x) / a, True))
return res.subs(x, a * x) / a
def test_octave_piecewise_times_const():
pw = Piecewise((x, x < 1), (x**2, True))
assert mcode(2 * pw) == "2*((x < 1).*(x) + (~(x < 1)).*(x.^2))"
assert mcode(pw / x) == "((x < 1).*(x) + (~(x < 1)).*(x.^2))./x"
assert mcode(pw / (x * y)) == "((x < 1).*(x) + (~(x < 1)).*(x.^2))./(x.*y)"
assert mcode(pw / 3) == "((x < 1).*(x) + (~(x < 1)).*(x.^2))/3"
def test_deltasummation_mul_add_x_y_add_kd_kd():
assert ds((x + y) * (KD(i, k) + KD(j, k)), (k, 1, 3)) == piecewise_fold(
Piecewise((x + y, And(Integer(1) <= i, i <= 3)), (0, True)) +
Piecewise((x + y, And(Integer(1) <= j, j <= 3)), (0, True)))
assert ds((x + y) * (KD(i, k) + KD(j, k)), (k, 1, 1)) == piecewise_fold(
Piecewise((x + y, Eq(i, 1)), (0, True)) +
Piecewise((x + y, Eq(j, 1)), (0, True)))
assert ds((x + y) * (KD(i, k) + KD(j, k)), (k, 2, 2)) == piecewise_fold(
Piecewise((x + y, Eq(i, 2)), (0, True)) +
Piecewise((x + y, Eq(j, 2)), (0, True)))
assert ds((x + y) * (KD(i, k) + KD(j, k)), (k, 3, 3)) == piecewise_fold(
Piecewise((x + y, Eq(i, 3)), (0, True)) +
Piecewise((x + y, Eq(j, 3)), (0, True)))
assert ds((x + y) * (KD(i, k) + KD(j, k)), (k, 1, l)) == piecewise_fold(
Piecewise((x + y, And(Integer(1) <= i, i <= l)), (0, True)) +
Piecewise((x + y, And(Integer(1) <= j, j <= l)), (0, True)))
assert ds((x + y) * (KD(i, k) + KD(j, k)), (k, l, 3)) == piecewise_fold(
Piecewise((x + y, And(l <= i, i <= 3)), (0, True)) +
Piecewise((x + y, And(l <= j, j <= 3)), (0, True)))
assert ds((x + y) * (KD(i, k) + KD(j, k)), (k, l, m)) == piecewise_fold(
Piecewise((x + y, And(l <= i, i <= m)), (0, True)) +
Piecewise((x + y, And(l <= j, j <= m)), (0, True)))
def test_rewrite_as_Piecewise():
x, y = symbols('x, y', real=True)
assert (Max(x, y).rewrite(Piecewise) == x * Piecewise(
(1, x - y > 0), (Rational(1, 2), Eq(x - y, 0)),
(0, true)) + y * Piecewise((1, -x + y > 0),
(Rational(1, 2), Eq(-x + y, 0)), (0, true)))
def roots_quartic(f):
r"""
Returns a list of roots of a quartic polynomial.
There are many references for solving quartic expressions available [1-5].
This reviewer has found that many of them require one to select from among
2 or more possible sets of solutions and that some solutions work when one
is searching for real roots but don't work when searching for complex roots
(though this is not always stated clearly). The following routine has been
tested and found to be correct for 0, 2 or 4 complex roots.
The quasisymmetric case solution [6] looks for quartics that have the form
`x**4 + A*x**3 + B*x**2 + C*x + D = 0` where `(C/A)**2 = D`.
Although no general solution that is always applicable for all
coefficients is known to this reviewer, certain conditions are tested
to determine the simplest 4 expressions that can be returned:
1) `f = c + a*(a**2/8 - b/2) == 0`
2) `g = d - a*(a*(3*a**2/256 - b/16) + c/4) = 0`
3) if `f != 0` and `g != 0` and `p = -d + a*c/4 - b**2/12` then
a) `p == 0`
b) `p != 0`
Examples
========
>>> from diofant import Poly, symbols, I
>>> r = roots_quartic(Poly('x**4-6*x**3+17*x**2-26*x+20'))
>>> # 4 complex roots: 1+-I*sqrt(3), 2+-I
>>> sorted(str(tmp.evalf(n=2)) for tmp in r)
['1.0 + 1.7*I', '1.0 - 1.7*I', '2.0 + 1.0*I', '2.0 - 1.0*I']
References
==========
.. [1] http://mathforum.org/dr.math/faq/faq.cubic.equations.html
.. [2] http://en.wikipedia.org/wiki/Quartic_function#Summary_of_Ferrari.27s_method
.. [3] http://planetmath.org/encyclopedia/GaloisTheoreticDerivationOfTheQuarticFormula.html
.. [4] http://staff.bath.ac.uk/masjhd/JHD-CA.pdf
.. [5] http://www.albmath.org/files/Math_5713.pdf
.. [6] http://www.statemaster.com/encyclopedia/Quartic-equation
.. [7] eqworld.ipmnet.ru/en/solutions/ae/ae0108.pdf
"""
_, a, b, c, d = f.monic().all_coeffs()
if not d:
return [S.Zero] + roots([1, a, b, c], multiple=True)
elif (c/a)**2 == d:
x, m = f.gen, c/a
g = Poly(x**2 + a*x + b - 2*m, x)
z1, z2 = roots_quadratic(g)
h1 = Poly(x**2 - z1*x + m, x)
h2 = Poly(x**2 - z2*x + m, x)
r1 = roots_quadratic(h1)
r2 = roots_quadratic(h2)
return r1 + r2
else:
a2 = a**2
e = b - 3*a2/8
f = c + a*(a2/8 - b/2)
g = d - a*(a*(3*a2/256 - b/16) + c/4)
aon4 = a/4
if f is S.Zero:
y1, y2 = [sqrt(tmp) for tmp in
roots([1, e, g], multiple=True)]
return [tmp - aon4 for tmp in [-y1, -y2, y1, y2]]
if g is S.Zero:
y = [S.Zero] + roots([1, 0, e, f], multiple=True)
return [tmp - aon4 for tmp in y]
else:
# Descartes-Euler method, see [7]
sols = _roots_quartic_euler(e, f, g, aon4)
if sols:
return sols
# Ferrari method, see [1, 2]
a2 = a**2
e = b - 3*a2/8
f = c + a*(a2/8 - b/2)
g = d - a*(a*(3*a2/256 - b/16) + c/4)
p = -e**2/12 - g
q = -e**3/108 + e*g/3 - f**2/8
TH = Rational(1, 3)
def _ans(y):
w = sqrt(e + 2*y)
arg1 = 3*e + 2*y
arg2 = 2*f/w
ans = []
for s in [-1, 1]:
root = sqrt(-(arg1 + s*arg2))
for t in [-1, 1]:
ans.append((s*w - t*root)/2 - aon4)
return ans
# p == 0 case
y1 = -5*e/6 - q**TH
if p.is_zero:
return _ans(y1)
# if p != 0 then u below is not 0
root = sqrt(q**2/4 + p**3/27)
r = -q/2 + root # or -q/2 - root
u = r**TH # primary root of solve(x**3 - r, x)
y2 = -5*e/6 + u - p/u/3
if p.is_nonzero:
return _ans(y2)
# sort it out once they know the values of the coefficients
return [Piecewise((a1, Eq(p, 0)), (a2, True))
for a1, a2 in zip(_ans(y1), _ans(y2))]
def test_Piecewise():
g = Piecewise((0, Or(x <= -1, x >= 1)), (1 - x, x > 0), (1 + x, True))
assert (mcode(g) ==
'Piecewise[{{0, x >= 1 || x <= -1}, '
'{-x + 1, x > 0}, {x + 1, True}}]')
def deltasummation(f, limit, no_piecewise=False):
"""Handle summations containing a KroneckerDelta.
The idea for summation is the following:
- If we are dealing with a KroneckerDelta expression, i.e. KroneckerDelta(g(x), j),
we try to simplify it.
If we could simplify it, then we sum the resulting expression.
We already know we can sum a simplified expression, because only
simple KroneckerDelta expressions are involved.
If we couldn't simplify it, there are two cases:
1) The expression is a simple expression: we return the summation,
taking care if we are dealing with a Derivative or with a proper
KroneckerDelta.
2) The expression is not simple (i.e. KroneckerDelta(cos(x))): we can do
nothing at all.
- If the expr is a multiplication expr having a KroneckerDelta term:
First we expand it.
If the expansion did work, then we try to sum the expansion.
If not, we try to extract a simple KroneckerDelta term, then we have two
cases:
1) We have a simple KroneckerDelta term, so we return the summation.
2) We didn't have a simple term, but we do have an expression with
simplified KroneckerDelta terms, so we sum this expression.
Examples
========
>>> from diofant import oo, symbols
>>> from diofant.abc import k
>>> i, j = symbols('i, j', integer=True, finite=True)
>>> from diofant import KroneckerDelta, Piecewise
>>> deltasummation(KroneckerDelta(i, k), (k, -oo, oo))
1
>>> deltasummation(KroneckerDelta(i, k), (k, 0, oo))
Piecewise((1, 0 <= i), (0, true))
>>> deltasummation(KroneckerDelta(i, k), (k, 1, 3))
Piecewise((1, And(1 <= i, i <= 3)), (0, true))
>>> deltasummation(k*KroneckerDelta(i, j)*KroneckerDelta(j, k), (k, -oo, oo))
j*KroneckerDelta(i, j)
>>> deltasummation(j*KroneckerDelta(i, j), (j, -oo, oo))
i
>>> deltasummation(i*KroneckerDelta(i, j), (i, -oo, oo))
j
See Also
========
deltaproduct
diofant.functions.special.tensor_functions.KroneckerDelta
diofant.concrete.sums.summation
"""
from diofant.concrete.summations import summation
from diofant.solvers import solve
if ((limit[2] - limit[1]) < 0) is S.true:
return S.Zero
if not f.has(KroneckerDelta):
return summation(f, limit)
x = limit[0]
g = _expand_delta(f, x)
if g.is_Add:
return piecewise_fold(
g.func(*[deltasummation(h, limit, no_piecewise) for h in g.args]))
# try to extract a simple KroneckerDelta term
delta, expr = _extract_delta(g, x)
if not delta:
return summation(f, limit)
solns = solve(delta.args[0] - delta.args[1], x)
if len(solns) == 0:
return S.Zero
elif len(solns) != 1:
return Sum(f, limit)
value = solns[0]
if no_piecewise:
return expr.subs(x, value)
return Piecewise(
(expr.subs(x, value), Interval(*limit[1:3]).as_relational(value)),
(S.Zero, True))