code: def solidangle(twotheta, sampletodetectordistance, pixelsize=None):
      
      if pixelsize is None:
          pixelsize = 1
      return sampletodetectordistance ** 2 / np.cos(twotheta) ** 3 / pixelsize ** 2
docs: Solid-angle correction for two-dimensional SAS images
  
      Inputs:
          twotheta: matrix of two-theta values
          sampletodetectordistance: sample-to-detector distance
          pixelsize: the pixel size in mm
  
      The output matrix is of the same shape as twotheta. The scattering intensity
          matrix should be multiplied by it.