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#!/opt/local/bin/python2.7 |
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'''An example script that generates a picture of the field lines for an electric quadrupole.''' |
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import math |
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import VectorFieldPlot as vfp |
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# create a document. we specify the file name and image size here |
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doc = vfp.FieldplotDocument( 'Quadrupole', width=800,height=600,unit=100) |
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# create a field opbject |
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field = vfp.Field() |
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# add the qpole |
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# note, parameters are should be [ r_x, r_y, phi, q], where r is the position vector, phi is the angle of the quadrupole in radians, and q is the charge magnitude |
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field.add_element('quadrupoles' , [ [ 0, 0, 0.0, 100] ] ) |
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# draw the charges for the field on the document |
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doc.draw_charges(field) |
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# start drawing the field lines |
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# we are going to draw 20 field lines comming off of the quadrupole at uniformly spaced angles. |
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N = 37 |
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for i in range(N): |
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# compute the angle that the line will start off at |
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angle = float(i) * 2.0* math.pi / float(N-1) |
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direction = 'forward' |
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if (math.fabs(angle - 0.0) < 1.0e-3): |
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direction = 'backwards' |
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if (math.fabs(angle - math.pi) < 1.0e-3): |
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direction = 'backwards' |
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print angle, direction |
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# generate the line this takes the initial position, the x and y |
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# components of the initial direction, and whether or not should |
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# go forward or backward. |
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line = vfp.FieldLine( field, [0.15*math.cos(angle),0.15*math.sin(angle)], start_v=[math.cos( angle ) , math.sin( angle )],directions=direction ) |
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# draw the lin on the document |
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doc.draw_line(line,arrows_style={'min_arrows':1,'scale':0.5,'max_arrows':2}) |
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# write the document |
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doc.write() |
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