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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 dipole.''' |
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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( 'PointCharges', 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 point charges |
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field.add_element('monopoles' , [ [ 1,0, 1] # the positive charge |
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, [-1,0,-1] # the negative charge |
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] ) |
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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 positive charge at uniformly spaced angles. |
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N = 20 |
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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 = i * 2.*math.pi / (N-1) |
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# generate the line |
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# this takes the initial position, the x and y components of the initial direction, and whether or not should go forward |
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# or backward. |
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line = vfp.FieldLine( field, [1,0], start_v=[math.cos( angle ) , math.sin( angle )],directions='forward' ) |
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# draw the lin on the document |
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doc.draw_line(line,arrows_style={'min_arrows':1,'scale':0.4,'max_arrows':3}) |
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# write the document |
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doc.write() |
