title: what is wrong with this shapely error message
body: <p>I have a dictionary called Rsize which have number-List as key-value pair. The dictionary is like this</p>
  
  <pre class="lang-py prettyprint-override"><code>{10: [0.6621485767296484, 0.6610747762560114, 0.659607022086639, 0.6567761845867727, 0.6535392433801197, 0.6485977028504701, 0.6393024556394106, 0.6223866436257335, 0.5999232392636733, 0.5418403536642005, 0.4961461379219235, 0.4280278015788386, 0.35462315989740956, 0.2863017237662875, 0.2312185739351389, 0.18306363413831017], 12: [0.6638977494825118, 0.663295576452323, 0.662262804664348, 0.6610413916318628, 0.6590939627030634, 0.655212304186114, 0.6492141689834672, 0.6380632834031537, 0.6096663492242224, 0.5647498006858608, 0.4983281599318278, 0.3961350546063216, 0.32119092575707087, 0.2257230704567207, 0.1816695139119151, 0.14363448808684576], 14: [0.6649598494971014, 0.6644370245269158, 0.6638578972784479, 0.6630511299276417, 0.6615070373022596, 0.6596206155163766, 0.6560628158033714, 0.6487119276511941, 0.6343385358239866, 0.5792725000508062, 0.49799837531709923, 0.42482204326408324, 0.26633662071414366, 0.2028085235063155, 0.12411214668987203, 0.09336935548451253]}
  [0.6621485767296484, 0.6610747762560114, 0.659607022086639, 0.6567761845867727, 0.6535392433801197, 0.6485977028504701, 0.6393024556394106, 0.6223866436257335, 0.5999232392636733, 0.5418403536642005, 0.4961461379219235, 0.4280278015788386, 0.35462315989740956, 0.2863017237662875, 0.2312185739351389, 0.18306363413831017]
  
  
  </code></pre>
  
  <p>The keys are 10,14,16. I have used each list for plotting and want to find out their pairwise intersection points. I have written the following script for that and used shapely intersection function for the intersection points detection.</p>
  
  <pre><code>from shapely.geometry import LineString
  Rsize={10: [0.6621485767296484, 0.6610747762560114, 0.659607022086639, 0.6567761845867727, 0.6535392433801197, 0.6485977028504701, 0.6393024556394106, 0.6223866436257335, 0.5999232392636733, 0.5418403536642005, 0.4961461379219235, 0.4280278015788386, 0.35462315989740956, 0.2863017237662875, 0.2312185739351389, 0.18306363413831017], 12: [0.6638977494825118, 0.663295576452323, 0.662262804664348, 0.6610413916318628, 0.6590939627030634, 0.655212304186114, 0.6492141689834672, 0.6380632834031537, 0.6096663492242224, 0.5647498006858608, 0.4983281599318278, 0.3961350546063216, 0.32119092575707087, 0.2257230704567207, 0.1816695139119151, 0.14363448808684576], 14: [0.6649598494971014, 0.6644370245269158, 0.6638578972784479, 0.6630511299276417, 0.6615070373022596, 0.6596206155163766, 0.6560628158033714, 0.6487119276511941, 0.6343385358239866, 0.5792725000508062, 0.49799837531709923, 0.42482204326408324, 0.26633662071414366, 0.2028085235063155, 0.12411214668987203, 0.09336935548451253]}
  [0.6621485767296484, 0.6610747762560114, 0.659607022086639, 0.6567761845867727, 0.6535392433801197, 0.6485977028504701, 0.6393024556394106, 0.6223866436257335, 0.5999232392636733, 0.5418403536642005, 0.4961461379219235, 0.4280278015788386, 0.35462315989740956, 0.2863017237662875, 0.2312185739351389, 0.18306363413831017]
  
  listkT = np.arange(4.0,4.8,0.05)
  
  print(Rsize[10])
  
  plt.figure(figsize=(18, 10))
  plt.title ('Binder cumulant for critical point')
  
  plt.plot(listkT, Rsize[10], '-',label='Lattice sie 10')
  plt.plot(listkT, Rsize[12], '-',label='Lattice sie 12')
  plt.plot(listkT, Rsize[14], '-',label='Lattice sie 14')
  plt.legend() 
  plt.show()
  
  curve_10=LineString(np.column_stack((listkT, Rsize[10])))
  curve_12=LineString(np.column_stack((listkT, Rsize[12])))
  curve_14=LineString(np.column_stack((listkT, Rsize[14])))
  
  intersection12 = curve_10.intersection(curve_12)
  intersection14 = curve_10.intersection(curve_14)
  
  plt.plot(*LineString(intersection12).xy, 'o')
  plt.plot(*LineString(intersection14).xy, 'o')
  
  x12, y = LineString(intersection12).xy
  x14, y = LineString(intersection14).xy
  print(np.intersect1d(x12, x14))
  print(x12,x14)
  </code></pre>
  
  <p>But shapely throws an AssertionError.</p>
  
  <pre><code>
    File "C:\Users\Endeavour\Anaconda3\lib\site-packages\spyder_kernels\customize\spydercustomize.py", line 827, in runfile
      execfile(filename, namespace)
  
    File "C:\Users\Endeavour\Anaconda3\lib\site-packages\spyder_kernels\customize\spydercustomize.py", line 110, in execfile
      exec(compile(f.read(), filename, 'exec'), namespace)
    File "E:/Project/Codes/3D.py", line 118, in &lt;module&gt;
      plt.plot(*LineString(intersection12).xy, 'o')
  
    File "C:\Users\Endeavour\Anaconda3\lib\site-packages\shapely\geometry\linestring.py", line 48, in __init__
      self._set_coords(coordinates)
  
    File "C:\Users\Endeavour\Anaconda3\lib\site-packages\shapely\geometry\linestring.py", line 97, in _set_coords
      ret = geos_linestring_from_py(coordinates)
  
    File "shapely/speedups/_speedups.pyx", line 87, in shapely.speedups._speedups.geos_linestring_from_py
  
  AssertionError
  </code></pre>
  
  <p>The plots are drawn correctly by matplotlib though.
  I am using shapely for first time with no prior experience in it. Any help will be much appreciated. Thank you.
  Note: The final goal is to get the intersection of 3 curves. If no intersection found the point where they come closest is good enough. Any suggestion or library function to find that will be of great help.</p>
  
  <p>Thank you in advance.</p>