Illustrates linear complementarity problem

Randall Romero Aguilar, PhD

This demo is based on the original Matlab demo accompanying the Computational Economics and Finance 2001 textbook by Mario Miranda and Paul Fackler.

Original (Matlab) CompEcon file: demslv10.m

Running this file requires the Python version of CompEcon. This can be installed with pip by running

!pip install compecon --upgrade

Last updated: 2021-Oct-01


import matplotlib.pyplot as plt
plt.style.use('seaborn')
def basicsubplot(ax, title, yvals,solution):
    ax.set(title=title,
           xlabel='',
           ylabel='',
           xlim=[-0.05,1.05],
           ylim=[-2,2],
           xticks=[0,1],
           xticklabels=['a','b'],
           yticks=[-2,0,2],
           yticklabels=['','0',''])

    ax.plot([0,1],[0,0],'k-',linewidth=1.5)
    ax.plot([0,0],[-2,2],'k:',linewidth=2.5)
    ax.plot([1,1],[-2,2],'k:',linewidth=2.5)
    ax.plot([0, 1],yvals)
    ax.plot(solution[0], solution[1],'r.', ms=18)

Possible Solutions to Complementarity Problem, \(f\) Strictly Decreasing

fig1, axs = plt.subplots(1,3,figsize=[9,4])
basicsubplot(axs[0],'f(a) > f(b) > 0', [1.5, 0.5], [1.0,0.5])
basicsubplot(axs[1],'f(a) > 0 > f(b)', [0.5, -0.5], [0.5,0.0])
basicsubplot(axs[2],'0 > f(a) > f(b)', [-0.5, -1.5],[0.0,-0.5])
../../_images/10 Illustrates linear complementarity problem_4_0.png

Possible Solutions to Complementarity Problem, \(f\) Strictly Increasing

fig2, axs = plt.subplots(1,3,figsize=[9,4])
basicsubplot(axs[0],'f(a) < f(b) < 0', [-1.5, -0.5], [0.0,-1.5])
basicsubplot(axs[1],'f(a) < 0 < f(b)', [-0.5, 0.5], [0.5,0.0])
basicsubplot(axs[2],'0 < f(a) < f(b)', [0.5, 1.5],[1.0,1.5])
axs[1].plot(0.0,-0.5,'r.',ms=18)
axs[1].plot(1.0,0.5,'r.',ms=18)
[<matplotlib.lines.Line2D at 0x18b70cc9b80>]
../../_images/10 Illustrates linear complementarity problem_6_1.png