78 lines
2.8 KiB
Python
78 lines
2.8 KiB
Python
import numpy as np
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import scipy.stats as st
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import matplotlib.pyplot as plt
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# normal distribution:
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x = np.arange( -3.0, 3.0, 0.01 )
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g = np.exp(-0.5*x*x)/np.sqrt(2.0*np.pi)
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plt.xkcd()
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fig = plt.figure( figsize=(6,3) )
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ax = fig.add_subplot(1, 2, 1)
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ax.spines['right'].set_visible(False)
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ax.spines['top'].set_visible(False)
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ax.yaxis.set_ticks_position('left')
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ax.xaxis.set_ticks_position('bottom')
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ax.set_xlabel( 'x' )
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ax.set_ylabel( 'Prob. density p(x)' )
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ax.set_ylim( 0.0, 0.46 )
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ax.set_yticks( np.arange( 0.0, 0.45, 0.1 ) )
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ax.text(-1.0, 0.06, '50%', ha='center' )
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ax.text(+1.0, 0.06, '50%', ha='center' )
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ax.annotate('Median\n= mean',
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xy=(0.1, 0.3), xycoords='data',
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xytext=(1.2, 0.35), textcoords='data', ha='left',
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arrowprops=dict(arrowstyle="->", relpos=(0.0,0.2),
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connectionstyle="angle3,angleA=10,angleB=40") )
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ax.annotate('Mode',
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xy=(-0.1, 0.4), xycoords='data',
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xytext=(-2.5, 0.43), textcoords='data', ha='left',
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arrowprops=dict(arrowstyle="->", relpos=(0.0,0.2),
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connectionstyle="angle3,angleA=10,angleB=120") )
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ax.fill_between( x[x<0], 0.0, g[x<0], color='#ffcc00' )
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ax.fill_between( x[x>0], 0.0, g[x>0], color='#99ff00' )
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ax.plot(x, g, 'b', lw=4)
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ax.plot([0.0, 0.0], [0.0, 0.45], 'k', lw=2 )
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# normal distribution:
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x = np.arange( 0.0, 6.0, 0.01 )
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shape = 2.0
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g = st.gamma.pdf(x, shape)
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m = st.gamma.median(shape)
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gm = st.gamma.mean(shape)
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ax = fig.add_subplot(1, 2, 2)
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ax.spines['right'].set_visible(False)
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ax.spines['top'].set_visible(False)
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ax.yaxis.set_ticks_position('left')
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ax.xaxis.set_ticks_position('bottom')
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ax.set_xlabel( 'x' )
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ax.set_ylabel( 'Prob. density p(x)' )
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ax.set_ylim( 0.0, 0.46 )
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ax.set_yticks( np.arange( 0.0, 0.45, 0.1 ) )
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ax.text(m-0.8, 0.06, '50%', ha='center' )
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ax.text(m+1.2, 0.06, '50%', ha='center' )
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ax.annotate('Median',
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xy=(m+0.1, 0.2), xycoords='data',
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xytext=(m+1.6, 0.25), textcoords='data', ha='left',
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arrowprops=dict(arrowstyle="->", relpos=(0.0,0.5),
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connectionstyle="angle3,angleA=30,angleB=70") )
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ax.annotate('Mean',
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xy=(gm, 0.01), xycoords='data',
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xytext=(gm+1.8, 0.15), textcoords='data', ha='left',
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arrowprops=dict(arrowstyle="->", relpos=(0.0,0.5),
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connectionstyle="angle3,angleA=0,angleB=90") )
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ax.annotate('Mode',
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xy=(1.0, 0.38), xycoords='data',
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xytext=(1.8, 0.42), textcoords='data', ha='left',
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arrowprops=dict(arrowstyle="->", relpos=(0.0,0.5),
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connectionstyle="angle3,angleA=0,angleB=70") )
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ax.fill_between( x[x<m], 0.0, g[x<m], color='#ffcc00' )
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ax.fill_between( x[x>m], 0.0, g[x>m], color='#99ff00' )
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ax.plot(x, g, 'b', lw=4)
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ax.plot([m, m], [0.0, 0.38], 'k', lw=2 )
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#ax.plot([gm, gm], [0.0, 0.42], 'k', lw=2 )
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plt.tight_layout()
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fig.savefig( 'median.pdf' )
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#plt.show()
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