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336 lines
11 KiB
336 lines
11 KiB
5 months ago
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from sympy.core import cacheit, Dummy, Ne, Integer, Rational, S, Wild
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from sympy.functions import binomial, sin, cos, Piecewise, Abs
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from .integrals import integrate
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# TODO sin(a*x)*cos(b*x) -> sin((a+b)x) + sin((a-b)x) ?
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# creating, each time, Wild's and sin/cos/Mul is expensive. Also, our match &
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# subs are very slow when not cached, and if we create Wild each time, we
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# effectively block caching.
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#
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# so we cache the pattern
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# need to use a function instead of lamda since hash of lambda changes on
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# each call to _pat_sincos
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def _integer_instance(n):
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return isinstance(n, Integer)
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@cacheit
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def _pat_sincos(x):
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a = Wild('a', exclude=[x])
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n, m = [Wild(s, exclude=[x], properties=[_integer_instance])
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for s in 'nm']
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pat = sin(a*x)**n * cos(a*x)**m
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return pat, a, n, m
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_u = Dummy('u')
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def trigintegrate(f, x, conds='piecewise'):
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"""
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Integrate f = Mul(trig) over x.
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Examples
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========
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>>> from sympy import sin, cos, tan, sec
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>>> from sympy.integrals.trigonometry import trigintegrate
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>>> from sympy.abc import x
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>>> trigintegrate(sin(x)*cos(x), x)
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sin(x)**2/2
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>>> trigintegrate(sin(x)**2, x)
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x/2 - sin(x)*cos(x)/2
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>>> trigintegrate(tan(x)*sec(x), x)
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1/cos(x)
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>>> trigintegrate(sin(x)*tan(x), x)
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-log(sin(x) - 1)/2 + log(sin(x) + 1)/2 - sin(x)
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References
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==========
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.. [1] https://en.wikibooks.org/wiki/Calculus/Integration_techniques
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See Also
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========
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sympy.integrals.integrals.Integral.doit
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sympy.integrals.integrals.Integral
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"""
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pat, a, n, m = _pat_sincos(x)
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f = f.rewrite('sincos')
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M = f.match(pat)
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if M is None:
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return
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n, m = M[n], M[m]
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if n.is_zero and m.is_zero:
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return x
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zz = x if n.is_zero else S.Zero
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a = M[a]
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if n.is_odd or m.is_odd:
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u = _u
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n_, m_ = n.is_odd, m.is_odd
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# take smallest n or m -- to choose simplest substitution
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if n_ and m_:
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# Make sure to choose the positive one
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# otherwise an incorrect integral can occur.
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if n < 0 and m > 0:
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m_ = True
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n_ = False
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elif m < 0 and n > 0:
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n_ = True
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m_ = False
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# Both are negative so choose the smallest n or m
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# in absolute value for simplest substitution.
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elif (n < 0 and m < 0):
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n_ = n > m
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m_ = not (n > m)
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# Both n and m are odd and positive
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else:
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n_ = (n < m) # NB: careful here, one of the
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m_ = not (n < m) # conditions *must* be true
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# n m u=C (n-1)/2 m
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# S(x) * C(x) dx --> -(1-u^2) * u du
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if n_:
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ff = -(1 - u**2)**((n - 1)/2) * u**m
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uu = cos(a*x)
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# n m u=S n (m-1)/2
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# S(x) * C(x) dx --> u * (1-u^2) du
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elif m_:
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ff = u**n * (1 - u**2)**((m - 1)/2)
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uu = sin(a*x)
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fi = integrate(ff, u) # XXX cyclic deps
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fx = fi.subs(u, uu)
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if conds == 'piecewise':
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return Piecewise((fx / a, Ne(a, 0)), (zz, True))
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return fx / a
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# n & m are both even
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#
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# 2k 2m 2l 2l
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# we transform S (x) * C (x) into terms with only S (x) or C (x)
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#
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# example:
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# 100 4 100 2 2 100 4 2
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# S (x) * C (x) = S (x) * (1-S (x)) = S (x) * (1 + S (x) - 2*S (x))
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#
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# 104 102 100
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# = S (x) - 2*S (x) + S (x)
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# 2k
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# then S is integrated with recursive formula
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# take largest n or m -- to choose simplest substitution
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n_ = (Abs(n) > Abs(m))
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m_ = (Abs(m) > Abs(n))
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res = S.Zero
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if n_:
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# 2k 2 k i 2i
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# C = (1 - S ) = sum(i, (-) * B(k, i) * S )
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if m > 0:
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for i in range(0, m//2 + 1):
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res += (S.NegativeOne**i * binomial(m//2, i) *
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_sin_pow_integrate(n + 2*i, x))
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elif m == 0:
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res = _sin_pow_integrate(n, x)
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else:
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# m < 0 , |n| > |m|
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# /
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# |
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# | m n
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# | cos (x) sin (x) dx =
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# |
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# |
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#/
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# /
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# |
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# -1 m+1 n-1 n - 1 | m+2 n-2
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# ________ cos (x) sin (x) + _______ | cos (x) sin (x) dx
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# |
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# m + 1 m + 1 |
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# /
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res = (Rational(-1, m + 1) * cos(x)**(m + 1) * sin(x)**(n - 1) +
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Rational(n - 1, m + 1) *
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trigintegrate(cos(x)**(m + 2)*sin(x)**(n - 2), x))
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elif m_:
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# 2k 2 k i 2i
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# S = (1 - C ) = sum(i, (-) * B(k, i) * C )
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if n > 0:
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# / /
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# | |
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# | m n | -m n
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# | cos (x)*sin (x) dx or | cos (x) * sin (x) dx
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# | |
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# / /
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#
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# |m| > |n| ; m, n >0 ; m, n belong to Z - {0}
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# n 2
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# sin (x) term is expanded here in terms of cos (x),
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# and then integrated.
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#
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for i in range(0, n//2 + 1):
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res += (S.NegativeOne**i * binomial(n//2, i) *
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_cos_pow_integrate(m + 2*i, x))
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elif n == 0:
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# /
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# |
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# | 1
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# | _ _ _
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# | m
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# | cos (x)
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# /
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#
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res = _cos_pow_integrate(m, x)
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else:
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# n < 0 , |m| > |n|
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# /
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# |
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# | m n
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# | cos (x) sin (x) dx =
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# |
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# |
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#/
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# /
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# |
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# 1 m-1 n+1 m - 1 | m-2 n+2
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# _______ cos (x) sin (x) + _______ | cos (x) sin (x) dx
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# |
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# n + 1 n + 1 |
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# /
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res = (Rational(1, n + 1) * cos(x)**(m - 1)*sin(x)**(n + 1) +
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Rational(m - 1, n + 1) *
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trigintegrate(cos(x)**(m - 2)*sin(x)**(n + 2), x))
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else:
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if m == n:
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##Substitute sin(2x)/2 for sin(x)cos(x) and then Integrate.
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res = integrate((sin(2*x)*S.Half)**m, x)
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elif (m == -n):
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if n < 0:
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# Same as the scheme described above.
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# the function argument to integrate in the end will
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# be 1, this cannot be integrated by trigintegrate.
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# Hence use sympy.integrals.integrate.
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res = (Rational(1, n + 1) * cos(x)**(m - 1) * sin(x)**(n + 1) +
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Rational(m - 1, n + 1) *
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integrate(cos(x)**(m - 2) * sin(x)**(n + 2), x))
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else:
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res = (Rational(-1, m + 1) * cos(x)**(m + 1) * sin(x)**(n - 1) +
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Rational(n - 1, m + 1) *
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integrate(cos(x)**(m + 2)*sin(x)**(n - 2), x))
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if conds == 'piecewise':
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return Piecewise((res.subs(x, a*x) / a, Ne(a, 0)), (zz, True))
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return res.subs(x, a*x) / a
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def _sin_pow_integrate(n, x):
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if n > 0:
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if n == 1:
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#Recursion break
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return -cos(x)
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# n > 0
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# / /
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# | |
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# | n -1 n-1 n - 1 | n-2
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# | sin (x) dx = ______ cos (x) sin (x) + _______ | sin (x) dx
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# | |
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# | n n |
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#/ /
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#
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#
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return (Rational(-1, n) * cos(x) * sin(x)**(n - 1) +
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Rational(n - 1, n) * _sin_pow_integrate(n - 2, x))
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if n < 0:
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if n == -1:
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##Make sure this does not come back here again.
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##Recursion breaks here or at n==0.
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return trigintegrate(1/sin(x), x)
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# n < 0
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# / /
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# | |
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# | n 1 n+1 n + 2 | n+2
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# | sin (x) dx = _______ cos (x) sin (x) + _______ | sin (x) dx
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# | |
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# | n + 1 n + 1 |
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#/ /
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#
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return (Rational(1, n + 1) * cos(x) * sin(x)**(n + 1) +
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Rational(n + 2, n + 1) * _sin_pow_integrate(n + 2, x))
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else:
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#n == 0
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#Recursion break.
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return x
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def _cos_pow_integrate(n, x):
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if n > 0:
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if n == 1:
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#Recursion break.
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return sin(x)
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# n > 0
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# / /
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# | |
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# | n 1 n-1 n - 1 | n-2
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# | sin (x) dx = ______ sin (x) cos (x) + _______ | cos (x) dx
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# | |
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# | n n |
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#/ /
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#
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return (Rational(1, n) * sin(x) * cos(x)**(n - 1) +
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Rational(n - 1, n) * _cos_pow_integrate(n - 2, x))
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if n < 0:
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if n == -1:
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##Recursion break
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return trigintegrate(1/cos(x), x)
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# n < 0
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# / /
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# | |
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# | n -1 n+1 n + 2 | n+2
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# | cos (x) dx = _______ sin (x) cos (x) + _______ | cos (x) dx
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# | |
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# | n + 1 n + 1 |
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#/ /
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#
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return (Rational(-1, n + 1) * sin(x) * cos(x)**(n + 1) +
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Rational(n + 2, n + 1) * _cos_pow_integrate(n + 2, x))
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else:
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# n == 0
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#Recursion Break.
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return x
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