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66 lines
1.8 KiB
Python
66 lines
1.8 KiB
Python
import numpy as np
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MAX_VAL = 1e3
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def kepler_potential(W_grid: np.ndarray,
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position_only: bool = False) -> np.ndarray:
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"""Computes the Kepler potential: V(R) = -G*m1*m2/R
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(assuming G = 1, m1 = 1, m2 = 1)
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assuming the point mass at (x = 0, y = 0).
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@params:
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- W: Phase-space vector
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- position_only: True if W is np.array([X, Y])
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@returns:
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- V: computed potential
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"""
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if position_only:
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X = W_grid[0]
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Y = W_grid[1]
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else:
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X = W_grid[0,0]
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Y = W_grid[0,1]
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# If X or Y is not an array (or a list), but rather a scalar, then we
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# create a list of one element so that it can work either way
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if np.ndim(X) == 0: X = np.array([X])
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if np.ndim(Y) == 0: Y = np.array([Y])
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R = np.sqrt(X**2 + Y**2)
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return -1/R
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def hh_potential(W_grid: np.ndarray,
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position_only=False) -> np.ndarray:
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"""Computes the Hénon-Heiles potential.
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:param W: Phase-space vector
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:output V: Potential
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"""
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if position_only:
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X = W_grid[0]
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Y = W_grid[1]
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else:
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X = W_grid[0, 0]
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Y = W_grid[0, 1]
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# If X or Y is not an array (or a list), but rather a scalar, then we
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# create a list of one element so that it can work either way
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if np.ndim(X) == 0: X = np.array([X])
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if np.ndim(Y) == 0: Y = np.array([Y])
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POT = (X**2 + Y**2 + 2*X**2*Y - 2*Y**3/3)/2
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return POT
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def hh_evolution(t: np.ndarray, W: np.ndarray):
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"""Computes the evolution from the HH potential
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:param t: Time (not used)
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:param W: Phase space vector
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:returns dot W: Time derivative of the phase space vector
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"""
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X = W[0 ,0]
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Y = W[0, 1]
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U = W[1, 0]
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V = W[1, 1]
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DX = U
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DY = V
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DU = -(2*X*Y + X)
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DV = -(X**2 - Y**2 + Y)
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return np.array([[DX, DY], [DU, DV]])
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