added python api
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import numpy as np
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import matplotlib.pyplot as plt
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import matplotlib.patches as patches
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import magpylib as mag
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import pyvista as pv
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class Magnet:
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def __init__(self, position, radius, height, direction, mag_strength):
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self.position = position # (x, y, z)
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self.radius = radius
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self.height = height
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self.direction = direction
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self.mag_strength = mag_strength
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def to_magpylib(self):
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return mag.magnet.Cylinder(
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magnetization=(0, 0, self.direction * self.mag_strength),
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dimension=(2 * self.radius, self.height),
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position=self.position
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)
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def plot_field_xz(collection, magnets, xlim, zlim, resolution=100, density=10, plot_type='fieldline', show=True):
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"""
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Plot the magnetic field lines in the XZ-plane (y=0).
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Parameters:
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- collection: Magpylib Collection
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- magnets: List of Magnet objects
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- xlim, zlim: Tuples defining plot limits
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- resolution: Grid resolution
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- density: Streamplot density
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"""
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print('computing plot, please wait (can take a minute or two)...')
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# Create grid in XZ-plane (Y=0)
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x = np.linspace(*xlim, resolution)
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z = np.linspace(*zlim, resolution)
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X, Z = np.meshgrid(x, z)
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Y = np.full_like(X, 2.5)
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positions = np.stack([X, Y, Z], axis=-1).reshape(-1, 3)
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# Calculate magnetic field
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B = collection.getB(positions).reshape(X.shape + (3,))
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BX = B[:, :, 0]
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BZ = B[:, :, 2]
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magnitude = np.linalg.norm([BX, BZ], axis=0)
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# Plot field lines
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plt.style.use('dark_background')
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fig, ax = plt.subplots(figsize=(10, 6))
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if plot_type == 'fieldline':
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stream = ax.streamplot(
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X, Z, BX, BZ,
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color=np.log(magnitude + 1e-12), # Avoid log(0)
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cmap='viridis',
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density=density,
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linewidth=1.0
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)
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plt.colorbar(stream.lines, label='Log( Field strength [T] )')
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elif plot_type == 'field_direction':
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qiver = ax.quiver(
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X, Z, BX/magnitude*0.04, BZ/magnitude*0.04,
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np.log(magnitude + 1e-12), # Avoid log(0)
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cmap='viridis',
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scale=2, # adjust to get good arrow length
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width=0.002, # arrow width
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pivot='middle' # arrow base in the middle of the vector
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)
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plt.colorbar(qiver, label='Log( Field strength [T] )')
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else:
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raise ValueError('Unknown visualiztaion type')
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ax.set_facecolor((0.1, 0.1, 0.1))
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ax.set_xlabel("X [mm]")
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ax.set_ylabel("Z [mm]")
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ax.set_title("Magnetic Field Lines in XZ Plane")
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ax.grid(False)
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fig.set_facecolor((0.1, 0.1, 0.1))
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# Draw magnets as transparent rectangles
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for m in magnets:
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x0 = m.position[0] - m.radius
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z0 = m.position[2] - m.height / 2
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# Draw semi-transparent white filled rectangle
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face_rect = patches.Rectangle(
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(x0, z0),
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width=2 * m.radius,
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height=m.height,
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facecolor='white',
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edgecolor='none',
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alpha=0.3
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)
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ax.add_patch(face_rect)
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# Draw opaque black edge rectangle on top
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edge_rect = patches.Rectangle(
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(x0, z0),
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width=2 * m.radius,
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height=m.height,
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facecolor='none',
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edgecolor='white',
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linewidth=1.0,
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alpha=1.0 # fully opaque edge
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)
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ax.add_patch(edge_rect)
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plt.tight_layout()
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if show:
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plt.show()
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def plot_field_rotation_xz_along_lines(collection, point_pairs, num_points=200, show=True):
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"""
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Plots magnetic field rotation angles in the XZ-plane along multiple lines.
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Parameters:
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- collection: Magpylib Collection
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- point_pairs: List of (start_point, end_point) tuples; each point is (x, y, z)
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- num_points: Number of samples along each line
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"""
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plt.style.use('dark_background')
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fig, ax = plt.subplots(figsize=(10, 4))
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colors = ['#4ea6ff', '#ff9933', '#4dd26a', '#ff5c5c', '#b88cf0', '#a67c6c', '#f291d0', '#aaaaaa']
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for idx, (point_start, point_end, label) in enumerate(point_pairs):
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# Generate points along the line
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line_points = np.linspace(point_start, point_end, num_points)
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# Compute magnetic field
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B = collection.getB(line_points)
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# Project B onto XZ plane
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B_xz = B[:, [0, 2]] # BX and BZ
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# Compute angle in XZ plane
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angles = -np.arctan2(B_xz[:, 1], B_xz[:, 0]) # angle in radians
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# Distance along the line
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distances = np.linalg.norm(line_points - point_start, axis=1)
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# Plot the curve
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color = colors[idx % len(colors)]
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ax.plot(distances, np.degrees(angles), color=color, linewidth=1.5, label=label)
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# Axis styling
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ax.set_xlabel("X [mm]")
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ax.set_ylabel("Field angle [degrees]")
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ax.set_title("Magnetic Field Rotation Along Lines in XZ Plane")
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ax.grid(True, linestyle='--', color='gray', linewidth=0.6, alpha=0.8)
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ax.set_facecolor((0.1, 0.1, 0.1))
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fig.set_facecolor((0.1, 0.1, 0.1))
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ax.legend()
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plt.tight_layout()
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if show:
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plt.show()
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# ----------------------------------------------------------------------------------------------------------------------
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def main():
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# Parameters
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num_magnets = 13
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spacing = 3 # mm between magnet centers
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radius = 1.4 # mm
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height = 4 # mm
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mag_strength = 800e3 # A/m
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show_3d_viewer = False # show 3d viewer with simulation scene
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plot_range = [spacing * num_magnets + 20, 30]
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# Create magnet objects
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magnets = []
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for i in range(num_magnets):
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direction = 1 if i % 2 == 0 else -1
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x_pos = (i - num_magnets / 2) * spacing
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position = [x_pos, 0, 0]
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magnets.append(Magnet(position, radius, height, direction, mag_strength))
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# Create Magpylib collection
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mag_sources = [m.to_magpylib() for m in magnets]
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collection = mag.Collection(mag_sources)
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# show 3d viewer with simulation scene
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if show_3d_viewer:
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pl = pv.Plotter()
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collection.show(backend='pyvista', canvas=pl)
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pl.set_background((0.1, 0.1, 0.1)) # solid black
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plane = pv.Plane(center=(0, 2.5, 0), direction=(0, 1, 0), i_size=plot_range[1], j_size=plot_range[0])
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pl.add_mesh(plane, color='white', opacity=0.7)
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pl.show()
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# Plot the field
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plot_field_xz(
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collection=collection,
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magnets=magnets,
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xlim=(-plot_range[0]/2, plot_range[0]/2),
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zlim=(-plot_range[1]/2, plot_range[1]/2),
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resolution=100,
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density=12,
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plot_type='fieldline', # 'field_direction' or 'fieldline'
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show=False
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)
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plot_field_rotation_xz_along_lines(collection, [((-8.9, 2.5, 4), (8, 2.5, 4), 'Z=4mm'),
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((-8.9, 2.5, 6), (8, 2.5, 6), 'Z=6mm'),
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((-8.9, 2.5, 8), (8, 2.5, 8), 'Z=8mm')],
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show=False)
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# show all plots
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plt.show()
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if __name__ == "__main__":
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main()
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