})
n = 20
for i in range(n):
a = -3 + 6 * (0.5 + i) / n
line = FieldLine(field, [a * scale, 6 * scale], maxr=12, pass_dipoles=1)
if abs((n - 1.) / 2. - i) > 7: off = 4 * [0.5]
else: off = 4 * [0.25]
doc.draw_line(line,
arrows_style={
'min_arrows': 2,
'max_arrows': 2,
'offsets': off,
'scale': 2.0
})
# draw the superconducting ball
ball = doc.draw_object('g', {'id': 'metal_ball'})
grad = doc.draw_object('radialGradient', {
'id': 'metal_spot',
'cx': '0.53',
'cy': '0.54',
'r': '0.55',
'fx': '0.65',
'fy': '0.7',
'gradientUnits': 'objectBoundingBox'
},
group=ball)
for col, of in (('#fff', 0), ('#e7e7e7', 0.15), ('#ddd', 0.25), ('#aaa', 0.7),
('#888', 0.9), ('#666', 1)):
doc.draw_object('stop', {'offset': of, 'stop-color': col}, group=grad)
doc.draw_object(
'circle', {
r = size * 1.0
exponent = 1.0 / 2.0 # run with exponent=1 to get a physically correct version
doc = FieldplotDocument('naughty-solenoid')
field = Field({'coils': [[0, 0, 0, r, l, 1]]})
n = 15
for i in range(n):
a = (0.5 + i) / n
a = (-1. + 2. * a)
# ... after this, a ranges approximately from -1 to 1
a = copysign(abs(a)**exponent, a)
# unphysical version for pedagogical use, students explain why it's impossible
# makes field more intense near the walls
# re copysign, see https://stackoverflow.com/questions/1986152/why-doesnt-python-have-a-sign-function
a = a * size
line = FieldLine(field, [0.0, a], directions='both', maxr=15.0)
doc.draw_line(line, arrows_style={'dist': 3, 'offsets': [0., .5, .5, 1.]})
doc.draw_object(
'path', {
'style': 'fill:none; stroke:#808080; ' +
'stroke-width:.06; stroke-linecap:butt',
'd': f'M -{l},-{r} L {l},-{r}'
})
doc.draw_object(
'path', {
'style': 'fill:none; stroke:#808080; ' +
'stroke-width:.06; stroke-linecap:butt',
'd': f'M -{l},{r} L {l},{r}'
})
doc.write()
line = FieldLine(field,
p0,
directions='both',
maxr=7,
path_close_tol=0.2,
hmax=0.1)
doc.draw_line(line,
arrows_style={
'dist': 1.8,
'max_arrows': 2,
'offsets': [0.9, 0.3, 0.3, 0.9]
})
first_sphere = False
# draw the spherical magnets
defs = doc.draw_object('defs', {})
grad = doc.draw_object('radialGradient', {
'id': 'grad',
'r': str(1.2 * R),
'cx': '0',
'cy': str(0.2 * R),
'fx': '0',
'fy': str(0.6 * R),
'gradientUnits': 'userSpaceOnUse'
},
group=defs)
for col, of, opa in [['#ffffff', '0', '0.66'], ['#ffffff', '0.04', '0.6'],
['#ffffff', '0.11', '0.4'], ['#ffffff', '0.22', '0.2'],
['#555555', '0.7', '0.3'], ['#000000', '1', '0.6']]:
stop = doc.draw_object('stop', {
'stop-color': col,