Python libmp.to_int函数代码示例

def npartitions(n, verbose=False):
    """
    Calculate the partition function P(n), i.e. the number of ways that
    n can be written as a sum of positive integers.

    P(n) is computed using the Hardy-Ramanujan-Rademacher formula,
    described e.g. at http://mathworld.wolfram.com/PartitionFunctionP.html

    The correctness of this implementation has been tested for 10**n
    up to n = 8.
    """
    n = int(n)
    if n < 0: return 0
    if n <= 5: return [1, 1, 2, 3, 5, 7][n]
    # Estimate number of bits in p(n). This formula could be tidied
    pbits = int((math.pi*(2*n/3.)**0.5-math.log(4*n))/math.log(10)+1)*\
        math.log(10,2)
    prec = p = int(pbits*1.1 + 100)
    s = fzero
    M = max(6, int(0.24*n**0.5+4))
    sq23pi = mpf_mul(mpf_sqrt(from_rational(2,3,p), p), mpf_pi(p), p)
    sqrt8 = mpf_sqrt(from_int(8), p)
    for q in xrange(1, M):
        a = A(n,q,p)
        d = D(n,q,p, sq23pi, sqrt8)
        s = mpf_add(s, mpf_mul(a, d), prec)
        if verbose:
            print "step", q, "of", M, to_str(a, 10), to_str(d, 10)
        # On average, the terms decrease rapidly in magnitude. Dynamically
        # reducing the precision greatly improves performance.
        p = bitcount(abs(to_int(d))) + 50
    np = to_int(mpf_add(s, fhalf, prec))
    return int(np)

def get_integer_part(expr, no, options, return_ints=False):
    """
    With no = 1, computes ceiling(expr)
    With no = -1, computes floor(expr)

    Note: this function either gives the exact result or signals failure.
    """

    # The expression is likely less than 2^30 or so
    assumed_size = 30
    ire, iim, ire_acc, iim_acc = evalf(expr, assumed_size, options)

    # We now know the size, so we can calculate how much extra precision
    # (if any) is needed to get within the nearest integer
    if ire and iim:
        gap = max(fastlog(ire) - ire_acc, fastlog(iim) - iim_acc)
    elif ire:
        gap = fastlog(ire) - ire_acc
    elif iim:
        gap = fastlog(iim) - iim_acc
    else:
        # ... or maybe the expression was exactly zero
        return None, None, None, None

    margin = 10

    if gap >= -margin:
        ire, iim, ire_acc, iim_acc = \
            evalf(expr, margin + assumed_size + gap, options)

    # We can now easily find the nearest integer, but to find floor/ceil, we
    # must also calculate whether the difference to the nearest integer is
    # positive or negative (which may fail if very close).
    def calc_part(expr, nexpr):
        nint = int(to_int(nexpr, rnd))
        n, c, p, b = nexpr
        if c != 1 and p != 0:
            expr = C.Add(expr, -nint, evaluate=False)
            x, _, x_acc, _ = evalf(expr, 10, options)
            try:
                check_target(expr, (x, None, x_acc, None), 3)
            except PrecisionExhausted:
                if not expr.equals(0):
                    raise PrecisionExhausted
                x = fzero
            nint += int(no*(mpf_cmp(x or fzero, fzero) == no))
        nint = from_int(nint)
        return nint, fastlog(nint) + 10

    re, im, re_acc, im_acc = None, None, None, None

    if ire:
        re, re_acc = calc_part(C.re(expr, evaluate=False), ire)
    if iim:
        im, im_acc = calc_part(C.im(expr, evaluate=False), iim)

    if return_ints:
        return int(to_int(re or fzero)), int(to_int(im or fzero))
    return re, im, re_acc, im_acc

 def calc_part(expr, nexpr):
     nint = int(to_int(nexpr, round_nearest))
     expr = C.Add(expr, -nint, evaluate=False)
     x, _, x_acc, _ = evalf(expr, 10, options)
     check_target(expr, (x, None, x_acc, None), 3)
     nint += int(no*(mpf_cmp(x or fzero, fzero) == no))
     nint = from_int(nint)
     return nint, fastlog(nint) + 10

 def calc_part(expr, nexpr):
     nint = int(to_int(nexpr, rnd))
     expr = C.Add(expr, -nint, evaluate=False)
     x, _, x_acc, _ = evalf(expr, 10, options)
     try:
         check_target(expr, (x, None, x_acc, None), 3)
     except PrecisionExhausted:
         if not expr.equals(0):
             raise PrecisionExhausted
         x = fzero
     nint += int(no * (mpf_cmp(x or fzero, fzero) == no))
     nint = from_int(nint)
     return nint, fastlog(nint) + 10

 def __int__(self):
     return int(mlib.to_int(self._mpf_))

 def ceiling(self):
     return C.Integer(int(mlib.to_int(mlib.mpf_ceil(self._mpf_, self._prec))))

 def floor(self):
     return C.Integer(int(mlib.to_int(mlib.mpf_floor(self._mpf_, self._prec))))