How to fill rainbow color under a curve in Python matplotlib

Question

I want to fill rainbow color under a curve. Actually the function matplotlib.pyplot.fill_between can fill area under a curve with a single color.

import mat         


        

Answer 1

Here is a modified solution of the accepted answer that uses trapezoids instead of rectangles.

import numpy as np
import pylab as plt

# a solution that uses rectangles
def rect(x,y,w,h,c):
    ax = plt.gca()
    polygon = plt.Rectangle((x,y),w,h,color=c)
    ax.add_patch(polygon)

# a solution that uses trapezoids
def polygon(x1,y1,x2,y2,c):
    ax = plt.gca()
    polygon = plt.Polygon( [ (x1,y1), (x2,y2), (x2,0), (x1,0) ], color=c )
    ax.add_patch(polygon)

def rainbow_fill(X,Y, cmap=plt.get_cmap("jet")):
    plt.plot(X,Y,lw=0)  # Plot so the axes scale correctly

    dx = X[1]-X[0]
    N  = float(X.size)

    for n, (x,y) in enumerate(zip(X,Y)):
        color = cmap(n/N)
        # uncomment to use rectangles
        # rect(x,0,dx,y,color)
        # uncomment to use trapezoids
        if n+1 == N: continue
        polygon(x,y,X[n+1],Y[n+1],color)

# Test data    
X = np.linspace(0,10,100)
Y = .25*X**2 - X
rainbow_fill(X,Y)
plt.show()