From aeea54c9acbc8945d0488526275d2f6692e20190 Mon Sep 17 00:00:00 2001
From: Sepehr Madani <ssepehrmadani@gmail.com>
Date: Tue, 1 Sep 2020 00:21:44 -0400
Subject: [PATCH] Implement Butterfly Algorithm
---
algorithms/butterfly_algorithm.py | 75 +++++++++++++++++++++++++++++++
1 file changed, 75 insertions(+)
create mode 100644 algorithms/butterfly_algorithm.py
diff --git a/algorithms/butterfly_algorithm.py b/algorithms/butterfly_algorithm.py
new file mode 100644
index 0000000..9a85a37
--- /dev/null
+++ b/algorithms/butterfly_algorithm.py
@@ -0,0 +1,75 @@
+from math import pi, cos, sin, radians
+from cmath import exp, phase
+from .base_algorithm import BaseAlgorithm
+
+from utils.pattern import compute_pattern, compute_single_pattern
+from utils.converter import vectorWrapToPi, wrapToPi
+
+class ButterflyAlgorithm(BaseAlgorithm):
+ """ Finds nulls by gradually widening the vectors
+ symmetrically (like a butterfly)to reduce the absolute
+ value of the pattern.
+ """
+
+ def __init__(self, options):
+ super().__init__(options)
+ self.main_ang = options.main_ang
+ self.null_degrees = options.null_degrees
+ self.bit_count = options.bit_count
+ self.bit_resolution = options.bit_resolution
+ self.pattern = 0
+
+ self.check_parameters()
+
+ def check_parameters(self):
+ super().check_parameters()
+ assert len(self.null_degrees) == 1
+
+ def get_pattern(self):
+ pattern_values = compute_pattern(
+ N=self.N,
+ k=self.k,
+ weights=[exp(1j * x) for x in self.vector_changes],
+ degrees=self.null_degrees,
+ use_absolute_value=False
+ )
+ self.pattern = pattern_values[0].conjugate()
+ print(f'{abs(self.pattern) = }')
+
+ def solve(self):
+ alpha = (2*pi) / (2**self.bit_resolution)
+
+ self.null_deg = self.null_degrees[0]
+ self.theta = pi * cos(radians(self.null_deg))
+ self.sum_dir = self.theta * (self.N - 1) / 2
+ self.vector_dirs = [k * self.theta for k in range(self.N)]
+ self.vector_diffs = vectorWrapToPi([x - self.sum_dir for x in self.vector_dirs])
+ self.vector_changes = [0 for _ in range(self.N)]
+
+ self.get_pattern()
+
+ hasTurned = False
+ while not hasTurned:
+ for idx in range(self.N // 2):
+ old_change = self.vector_changes[:]
+ other = self.N - 1 - idx
+ angle_with_sum = wrapToPi(self.vector_diffs[idx] + self.vector_changes[idx])
+
+ if 0 <= angle_with_sum < pi - alpha/2:
+ self.vector_changes[idx] += alpha
+ self.vector_changes[other] -= alpha
+ elif -pi + alpha/2 < angle_with_sum <= 0:
+ self.vector_changes[idx] -= alpha
+ self.vector_changes[other] += alpha
+
+ self.vector_diffs = vectorWrapToPi(self.vector_diffs)
+ self.vector_changes = vectorWrapToPi(self.vector_changes)
+
+ self.get_pattern()
+
+ if (hasTurned := abs(cos(phase(self.pattern) - self.sum_dir) + 1) < 1e-9):
+ break
+
+ self.vector_changes = old_change[:]
+ self.get_pattern()
+
--
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