<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def calculate_squared_differences(image_tile_dict, transformed_array, template, sq_diff_tolerance=0.1):
 """As above, but for when the squared differences matching method is used """

    template_norm_squared = np.sum(template**2)
    image_norms_squared = {(x,y):np.sum(image_tile_dict[(x,y)]**2) for (x,y) in image_tile_dict.keys()}
    match_points = image_tile_dict.keys()
    # for correlation, then need to transofrm back to get correct value for division
    h, w = template.shape
    image_matches_normalised = {match_points[i]:-2*transformed_array[match_points[i][0], match_points[i][1]] + image_norms_squared[match_points[i]] + template_norm_squared for i in range(len(match_points))}
    #print image_matches_normalised
    cutoff = h*w*255**2*sq_diff_tolerance
    normalised_matches = {key:value for key, value in image_matches_normalised.items() if np.round(value, decimals=3) <= cutoff}
    return normalised_matches.keys()