Summary

{{Information

|description=

|date=2017-05-01 |source=Own work |author=Geek3 |permission= |other versions= with electric current symbols |other fields={{Igen|VectorFieldPlot|0|+|c1=

1. paste this code at the end of VectorFieldPlot 1.4

import scipy.optimize as op

M = 1.0 # magnetic moment r = 0.65; l = 1.2 n = 10 fieldB = Field({'coils':0, 0, 0, r, l, M/(r**2*pi)}) fieldH = Field({'charged_discs':[[-l, -r, -l, r, -0.5*M/l],

                                [ l, -r,  l, r,  0.5*M/l]]})

inside = lambda p: -min(1-fabs(p[0]/l), 1-fabs(p[1]/r)) outside = lambda p: min(1-fabs(p[0]/l), 1-fabs(p[1]/r))

for field in ['B', 'H']:

   fname = 'VFPt_magnet_' + field
   doc = FieldplotDocument(fname, width=400, height=300, commons=True)
   
   for i in range(n):
       r_rel = 2 * (0.5 + i) / n - 1
       y0 = r * (r_rel + 0.16 * (r_rel - r_rel**3))
       p0 = sc.array([l, y0])
       line1 = FieldLine(fieldB, p0*(1+1e-9), directions='forward',
                         maxr=1e4, maxn=1e4, stop_funcs=2*[outside])
       doc.draw_line(line1, arrows_style={})
       
       # B-field inside magnet
       line2 = FieldLine(fieldB, p0*(1-1e-9), directions='backward',
                         stop_funcs=2*[inside])
       if field == 'B':
           doc.draw_line(line2, arrows_style={})
       
       # H-field inside magnet
       line3 = FieldLine(fieldH, p0*(1-1e-9), directions='forward',
           stop_funcs=2*[inside])
       if field == 'H':
           doc.draw_line(line3, arrows_style={
                         'min_arrows':0, 'dist':0.6, 'max_arrows':2})
       
       p1 = line3.nodes[-1]['p'] # where lines leave the magnet on the side
       if fabs(p1[1]) >= r * (1-1e-8):
           p1[1] = copysign(max(r, fabs(p1[1])), p1[1])
           line4 = FieldLine(fieldH, p1, directions='forward',
                             stop_funcs=2*[outside])
           doc.draw_line(line4, arrows_style={'max_arrows':2})
           
           p2 = line4.nodes[-1]['p'] # where lines re-enter the magnet
           line5 = FieldLine(fieldH, p2, directions='forward',
                             stop_funcs=2*[inside])
           if field == 'H':
               doc.draw_line(line5, arrows_style={
                             'min_arrows':0, 'dist':0.6, 'max_arrows':2})
           
           line6 = FieldLine(fieldB, p1*(1-1e-9), directions='backward',
                             stop_funcs=2*[inside])
           if field == 'B':
               doc.draw_line(line6, arrows_style={})
   
   if field == 'H':
       doc.draw_object('path', {'d':'M {},{} V {} M {},{} V {}'.format(
       -l, -r, r, l, -r, r), 'style':'stroke:#999999; stroke-width:0.02'})
   
   doc.draw_magnets(fieldB)
   
   # postprocessing: strip text and add opacity
   for el in doc.svg.iter():
       if el.tag.endswith('g'):
           if el.get('id') != None and 'magnet' in el.get('id'):
               el.set('opacity', '0.4')
       if el.tag.endswith('text'):
           el.getparent().remove(el)
   
   doc.write()

}} }}

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