如何在Matplotlib中添加第二个X轴 [英] How to add a second x-axis in matplotlib

问题描述

我有一个非常简单的问题.我需要在绘图上有第二个x轴，并且希望该轴具有一定数量的tic，它们对应于第一个x轴的特定位置.

I have a very simple question. I need to have a second x-axis on my plot and I want that this axis has a certain number of tics that correspond to certain position of the first axis.

让我们尝试一个例子.在这里，我将暗物质质量与膨胀因子(定义为1/(1 + z)，范围从0到1)的函数作图.

Let's try with an example. Here I am plotting the dark matter mass as a function of the expansion factor, defined as 1/(1+z), that ranges from 0 to 1.

semilogy(1/(1+z),mass_acc_massive,'-',label='DM')
xlim(0,1)
ylim(1e8,5e12)

我想在图的顶部显示另一个x轴，以显示对应于某些膨胀系数值的z轴.那可能吗?如果是的话，我怎么能拥有xtics斧

I would like to have another x-axis, on the top of my plot, showing the corresponding z for some values of the expansion factor. Is that possible? If yes, how can I have xtics ax

推荐答案

我正在从@Dhara答案中的注释中获取线索，这听起来像是您希望通过旧函数设置new_tick_locations的列表x轴到新的x轴.下面的tick_function接收点的numpy数组，将它们映射为新值并设置其格式:

I'm taking a cue from the comments in @Dhara's answer, it sounds like you want to set a list of new_tick_locations by a function from the old x-axis to the new x-axis. The tick_function below takes in a numpy array of points, maps them to a new value and formats them:

import numpy as np
import matplotlib.pyplot as plt

fig = plt.figure()
ax1 = fig.add_subplot(111)
ax2 = ax1.twiny()

X = np.linspace(0,1,1000)
Y = np.cos(X*20)

ax1.plot(X,Y)
ax1.set_xlabel(r"Original x-axis: $X$")

new_tick_locations = np.array([.2, .5, .9])

def tick_function(X):
    V = 1/(1+X)
    return ["%.3f" % z for z in V]

ax2.set_xlim(ax1.get_xlim())
ax2.set_xticks(new_tick_locations)
ax2.set_xticklabels(tick_function(new_tick_locations))
ax2.set_xlabel(r"Modified x-axis: $1/(1+X)$")
plt.show()

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