在作圖過程中，需要繪制多個變量，但是每個變量的數量級不同，在一個坐標軸下作圖導致曲線變化很難觀察，這時就用到多個坐標軸。本文除了涉及多個坐標軸還包括Axisartist相關作圖指令、做圖中label為公式的表達方式、matplotlib中常用指令。

一、放一個官方例子先

from mpl_toolkits.axisartist.parasite_axes import HostAxes, ParasiteAxesimport matplotlib.pyplot as pltimport numpy as npfig = plt.figure(1) #定義figure，（1）中的1是什么ax_cof = HostAxes(fig, [0, 0, 0.9, 0.9]) #用[left, bottom, weight, height]的方式定義axes，0 <= l,b,w,h <= 1#parasite addtional axes, share xax_temp = ParasiteAxes(ax_cof, sharex=ax_cof)ax_load = ParasiteAxes(ax_cof, sharex=ax_cof)ax_cp = ParasiteAxes(ax_cof, sharex=ax_cof)ax_wear = ParasiteAxes(ax_cof, sharex=ax_cof)#append axesax_cof.parasites.append(ax_temp)ax_cof.parasites.append(ax_load)ax_cof.parasites.append(ax_cp)ax_cof.parasites.append(ax_wear)#invisible right axis of ax_cofax_cof.axis[’right’].set_visible(False)ax_cof.axis[’top’].set_visible(False)ax_temp.axis[’right’].set_visible(True)ax_temp.axis[’right’].major_ticklabels.set_visible(True)ax_temp.axis[’right’].label.set_visible(True)#set label for axisax_cof.set_ylabel(’cof’)ax_cof.set_xlabel(’Distance (m)’)ax_temp.set_ylabel(’Temperature’)ax_load.set_ylabel(’load’)ax_cp.set_ylabel(’CP’)ax_wear.set_ylabel(’Wear’)load_axisline = ax_load.get_grid_helper().new_fixed_axiscp_axisline = ax_cp.get_grid_helper().new_fixed_axiswear_axisline = ax_wear.get_grid_helper().new_fixed_axisax_load.axis[’right2’] = load_axisline(loc=’right’, axes=ax_load, offset=(40,0))ax_cp.axis[’right3’] = cp_axisline(loc=’right’, axes=ax_cp, offset=(80,0))ax_wear.axis[’right4’] = wear_axisline(loc=’right’, axes=ax_wear, offset=(120,0))fig.add_axes(ax_cof)’’’ #set limit of x, yax_cof.set_xlim(0,2)ax_cof.set_ylim(0,3)’’’curve_cof, = ax_cof.plot([0, 1, 2], [0, 1, 2], label='CoF', color=’black’)curve_temp, = ax_temp.plot([0, 1, 2], [0, 3, 2], label='Temp', color=’red’)curve_load, = ax_load.plot([0, 1, 2], [1, 2, 3], label='Load', color=’green’)curve_cp, = ax_cp.plot([0, 1, 2], [0, 40, 25], label='CP', color=’pink’)curve_wear, = ax_wear.plot([0, 1, 2], [25, 18, 9], label='Wear', color=’blue’)ax_temp.set_ylim(0,4)ax_load.set_ylim(0,4)ax_cp.set_ylim(0,50)ax_wear.set_ylim(0,30)ax_cof.legend()#軸名稱，刻度值的顏色#ax_cof.axis[’left’].label.set_color(ax_cof.get_color())ax_temp.axis[’right’].label.set_color(’red’)ax_load.axis[’right2’].label.set_color(’green’)ax_cp.axis[’right3’].label.set_color(’pink’)ax_wear.axis[’right4’].label.set_color(’blue’)ax_temp.axis[’right’].major_ticks.set_color(’red’)ax_load.axis[’right2’].major_ticks.set_color(’green’)ax_cp.axis[’right3’].major_ticks.set_color(’pink’)ax_wear.axis[’right4’].major_ticks.set_color(’blue’)ax_temp.axis[’right’].major_ticklabels.set_color(’red’)ax_load.axis[’right2’].major_ticklabels.set_color(’green’)ax_cp.axis[’right3’].major_ticklabels.set_color(’pink’)ax_wear.axis[’right4’].major_ticklabels.set_color(’blue’)ax_temp.axis[’right’].line.set_color(’red’)ax_load.axis[’right2’].line.set_color(’green’)ax_cp.axis[’right3’].line.set_color(’pink’)ax_wear.axis[’right4’].line.set_color(’blue’)plt.show()

該例子的作圖結果為：

二、實際繪制

在實際使用中希望繪制的多變量數值如下表所示：

為了實現這個作圖，經過反復修改美化，代碼如下：

1.導入包

from mpl_toolkits.axisartist.parasite_axes import HostAxes, ParasiteAxesimport matplotlib.pyplot as plt

2.導入數據

x = [’ATL’,’LAX’,’CLT’,’LAS’,’MSP’,’DTW’,’PHX’,’DCA’,’SLC’,’ORD’,’DFW’,’PHL’,’PDX’,’DEN’,’IAH’,’BOS’,’SAN’,’BWI’,’MDW’,’IND’]k_in = [49.160,47.367,26.858,30.315,16.552,28.590,23.905,18.818,28.735,6.721,10.315,26.398,38.575,7.646,11.227,8.864,15.327,19.120,11.521,19.618]k_out = [38.024,19.974,25.011,22.050,30.108,18.327,20.811,28.464,23.72,8.470,4.119,10.000,25.158,7.851,10.450,11.130,15.441,7.519,20.819,32.825]p = [0.0537,0.0301,0.0306,0.0217,0.0229,0.0223,0.0218,0.0179,0.0155,0.0465,0.0419,0.0165,0.0091,0.0357,0.0232,0.0200,0.0129,0.0143,0.0113,0.0064]K = [4.6844,2.0296,1.5858,1.1347,1.0706,1.0442,0.9764,0.8447,0.8141,0.7066,0.6041,0.5990,0.5808,0.5534,0.5023,0.3992,0.3964,0.3799,0.3639,0.3331]

3.作圖并保存，相關指令后有備注，可以幫助理解

fig = plt.figure(1) #定義figureax_k = HostAxes(fig, [0, 0, 0.9, 0.9]) #用[left, bottom, weight, height]的方式定義axes，0 <= l,b,w,h <= 1#parasite addtional axes, share xax_p = ParasiteAxes(ax_k, sharex=ax_k)ax_K = ParasiteAxes(ax_k, sharex=ax_k)#append axesax_k.parasites.append(ax_p)ax_k.parasites.append(ax_K)ax_k.set_ylabel(’$K_i^{in};/;K_i^{out}$’)ax_k.axis[’bottom’].major_ticklabels.set_rotation(45)ax_k.set_xlabel(’Airport’)ax_k.axis[’bottom’,’left’].label.set_fontsize(12) # 設置軸label的大小ax_k.axis[’bottom’].major_ticklabels.set_pad(8) #設置x軸坐標刻度與x軸的距離，坐標軸刻度旋轉會使label和坐標軸重合ax_k.axis[’bottom’].label.set_pad(12) #設置x軸坐標刻度與x軸label的距離，label會和坐標軸刻度重合ax_k.axis[:].major_ticks.set_tick_out(True) #設置坐標軸上刻度突起的短線向外還是向內#invisible right axis of ax_kax_k.axis[’right’].set_visible(False)ax_k.axis[’top’].set_visible(True)ax_p.axis[’right’].set_visible(True)ax_p.axis[’right’].major_ticklabels.set_visible(True)ax_p.axis[’right’].label.set_visible(True)ax_p.axis[’right’].major_ticks.set_tick_out(True)ax_p.set_ylabel(’${p_i}$’)ax_p.axis[’right’].label.set_fontsize(13)ax_K.set_ylabel(’${K_i}$’)K_axisline = ax_K.get_grid_helper().new_fixed_axisax_K.axis[’right2’] = K_axisline(loc=’right’, axes=ax_K, offset=(60,0))ax_K.axis[’right2’].major_ticks.set_tick_out(True)ax_K.axis[’right2’].label.set_fontsize(13)fig.add_axes(ax_k)curve_k1, = ax_k.plot(list(range(20)), k_in, marker =’v’,markersize=8,label='$K_i^{in}$',alpha = 0.7)curve_k2, = ax_k.plot(list(range(20)), k_out, marker =’^’,markersize=8, label='$K_i^{out}$',alpha = 0.7)curve_p, = ax_p.plot(list(range(20)), p, marker =’P’,markersize=8,label='${p_i}$',alpha = 0.7)curve_K, = ax_K.plot(list(range(20)), K, marker =’o’,markersize=8, label='${K_i}$',alpha = 0.7,linewidth=3)plt.xticks(list(range(20)), x)# ax_k.set_xticks(list(range(20))) # ax_k.set_xticklabels(x)ax_k.axis[’bottom’].major_ticklabels.set_rotation(45)# ax_k.set_rotation(90)# plt.xticks(list(range(20)), x, rotation = ’vertical’)ax_p.set_ylim(0,0.06)ax_K.set_ylim(0,5)ax_k.legend(labelspacing = 0.4, fontsize = 10)#軸名稱，刻度值的顏色 ax_p.axis[’right’].label.set_color(curve_p.get_color()) # 坐標軸label的顏色ax_K.axis[’right2’].label.set_color(curve_K.get_color())ax_p.axis[’right’].major_ticks.set_color(curve_p.get_color()) # 坐標軸刻度小突起的顏色ax_K.axis[’right2’].major_ticks.set_color(curve_K.get_color())ax_p.axis[’right’].major_ticklabels.set_color(curve_p.get_color()) # 坐標軸刻度值的顏色ax_K.axis[’right2’].major_ticklabels.set_color(curve_K.get_color())ax_p.axis[’right’].line.set_color(curve_p.get_color()) # 坐標軸線的顏色ax_K.axis[’right2’].line.set_color(curve_K.get_color())plt.savefig(’10.key metrics mapping.pdf’, bbox_inches=’tight’, dpi=800)plt.show()

4.繪制結果

PS

該作圖是在Axisartist的基礎上完成的，一些平時常用的繪制指令在此處是無用的。經過查找相關資料，https://www.osgeo.cn/matplotlib/tutorials/toolkits/axisartist.html 該網站可以提供一些用法的幫助。

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