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Python function that plots the data from a traveling salesman problem that I am working on for a discrete optimization class on Coursera. It can take multiple iterations of the path between nodes and plot out the current path as well as the old paths. Helps with troubleshooting and improving the algorithms that I am working on.
import matplotlib.pyplot as plt
def plotTSP(path, points, num_iters=1):
path: List of lists with the different orders in which the nodes are visited
points: coordinates for the different nodes
num_iters: number of paths that are in the path list
# Unpack the primary TSP path and transform it into a list of ordered
# coordinates
x = []; y = []
for i in paths[0]:
plt.plot(x, y, 'co')
# Set a scale for the arrow heads (there should be a reasonable default for this, WTF?)
a_scale = float(max(x))/float(100)
# Draw the older paths, if provided
if num_iters > 1:
for i in range(1, num_iters):
# Transform the old paths into a list of coordinates
xi = []; yi = [];
for j in paths[i]:
plt.arrow(xi[-1], yi[-1], (xi[0] - xi[-1]), (yi[0] - yi[-1]),
head_width = a_scale, color = 'r',
length_includes_head = True, ls = 'dashed',
width = 0.001/float(num_iters))
for i in range(0, len(x) - 1):
plt.arrow(xi[i], yi[i], (xi[i+1] - xi[i]), (yi[i+1] - yi[i]),
head_width = a_scale, color = 'r', length_includes_head = True,
ls = 'dashed', width = 0.001/float(num_iters))
# Draw the primary path for the TSP problem
plt.arrow(x[-1], y[-1], (x[0] - x[-1]), (y[0] - y[-1]), head_width = a_scale,
color ='g', length_includes_head=True)
for i in range(0,len(x)-1):
plt.arrow(x[i], y[i], (x[i+1] - x[i]), (y[i+1] - y[i]), head_width = a_scale,
color = 'g', length_includes_head = True)
#Set axis too slitghtly larger than the set of x and y
plt.xlim(0, max(x)*1.1)
plt.ylim(0, max(y)*1.1)
if __name__ == '__main__':
# Run an example
# Create a randomn list of coordinates, pack them into a list
x_cor = [1, 8, 4, 9, 2, 1, 8]
y_cor = [1, 2, 3, 4, 9, 5, 7]
points = []
for i in range(0, len(x_cor)):
points.append((x_cor[i], y_cor[i]))
# Create two paths, teh second with two values swapped to simulate a 2-OPT
# Local Search operation
path4 = [0, 1, 2, 3, 4, 5, 6]
path3 = [0, 2, 1, 3, 4, 5, 6]
path2 = [0, 2, 1, 3, 6, 5, 4]
path1 = [0, 2, 1, 3, 6, 4, 5]
# Pack the paths into a list
paths = [path1, path2, path3, path4]
# Run the function
plotTSP(paths, points, 4)
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osteth commented May 8, 2016

Hey, I wrote myself a little attempt at a novel TSP solver, I need a way of visualizing the output so I can easily check over its results. I am producing an output that is a list of lists that is ordered coordinates for the path. I'm not sure what the points and num-iters is for in your code and am having some trouble adapting it over. (could just be because of my lack of coding experience) but I was wondering if you would be willing to help me figure out how to adapt this into my program.

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tnlin commented Aug 12, 2016

It means how many path you wanna show on this plot
BTW, There are typo in line 3: path"s"

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peter-dye commented Jul 21, 2020

Thanks! This was really helpful to visualize what was going on in my ant colony system TSP solution. Just FYI the parameter "path" in the function definition should be "paths" to match the function body.

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