import math


def get_fig_size(fig_width_cm, fig_height_cm=None):
    """Convert dimensions in centimeters to inches.
    If no height is given, it is computed using the golden ratio.
    """
    if not fig_height_cm:
        golden_ratio = (1 + math.sqrt(5))/2
        fig_height_cm = fig_width_cm / golden_ratio

    size_cm = (fig_width_cm, fig_height_cm)
    return map(lambda x: x/2.54, size_cm)