code: def apply_fit(xy,coeffs):
      
      x_new = coeffs[0][2] + coeffs[0][0]*xy[:,0] + coeffs[0][1]*xy[:,1]
      y_new = coeffs[1][2] + coeffs[1][0]*xy[:,0] + coeffs[1][1]*xy[:,1]
  
      return x_new,y_new
docs: Apply the coefficients from a linear fit to
          an array of x,y positions.
  
          The coeffs come from the 'coeffs' member of the
          'fit_arrays()' output.