python中带有颜色渐变的图形

Question

I'm solving some equations of motion in Python, but I found some problems when wanting to plot my results.

I have different curves of phase space, ie velocity versus position curves and I'm using Pyplot to graph them.

I would like to graph them using a gradient of colors, like the figure below.

This chart was made in Matlab, however with Python I can not repeat the same graph. At most I have the following:

Where each line of the graphic is a curve different phase space, it is the same curve. Then the code I'm using to plot:

import matplotlib              
import matplotlib.mlab as mlab 
import matplotlib.pyplot as plt

plt.figure()
#plt.title('Distribucion de velocidades en el slower Li-7')
for i in range(0,199):
    plt.plot(res_s7[i],res_v7[i],color="blue")
plt.ylim([-100,1000])
plt.xlim([-0.1,0.6])
plt.xlabel('Posicion [m]')
plt.ylabel('Velocidad [m/s]')

Where res_s7 and res_v7 [i] arrangements represents the ith phase space curve.

I hope I was clear enough with what I want, and I hope you can help me, thank you very much in advance!

Answer 1

You can calculate the color of each line, eg calculating Red-Green-Blue values, each in the interval [0,1]:

import matplotlib.pyplot as plt

plt.figure()
for i in range(0,19):
    plt.plot((-0.1, 0.6),(i, i), color=((20-i)/20., 0, i/20.)) 
plt.ylim([0,20]) 
plt.xlim([-0.1,0.6]) 
plt.xlabel('Posicion [m]')      
plt.ylabel('Velocidad [m/s]') 
plt.show()

Also look into specifying a colorbar and choosing color values as a position in the colorbar -- that will let you adapt quickly to different journals' standards, or colorblindness-kind representations, etc. To do that, check out one of the matplotlib LineCollection examples : collections are nice to work with in the long run, and you've already organized your data well for them in res_?7. The colormap is a property of the LineCollection, which adds one line to the example:

line_segments.set_array(x)
line_segments.set_cmap(cm.coolwarm)  #this is the new line
ax.add_collection(line_segments)

result:

Answer 2

You can get a color from colormaps defined in 'matplotlib.cm`. For example, some blue-red colormap I found at http://matplotlib.org/users/colormaps.html was seismic.

import matplotlib              
import matplotlib.mlab as mlab 
import matplotlib.pyplot as plt
import matplotlib.cm as cm

plt.figure()
#plt.title('Distribucion de velocidades en el slower Li-7')
for i in range(0,199):
    plt.plot(res_s7[i],res_v7[i],color=cm.seismic(i))
plt.ylim([-100,1000])
plt.xlim([-0.1,0.6])
plt.xlabel('Posicion [m]')
plt.ylabel('Velocidad [m/s]')