How to plot recursive function in matplotlib.pyplot?

Question

I'm trying to plot a recursive function I had made that measures growth over time. Here is the function:

def pop(start_pop, years, percentage_change, max_pop):
    if years == 0:
         return start_pop
    else:
         changes = pop(start_pop,years-1,percentage_change,max_pop)
         return changes + (1-changes/max_pop)*percentage_change*changes

print(pop(600,85,0.1,20000))

Which gives me the output of:

19879.4425

How can I plot this function of the graph, where "years" is on the x-axis and "max_pop" is on the y-axis?

Thanks for your help!

Note: If it helps, I'm wanting/ expecting once plotted that the curve will look something similar to a learning curve.

If you want to plot a function f(x, otherargs) at values x = [1,2,3,...] you evaluate the function on the list, e.g. y = [f(i, otherargs) for i in x] and plot plt.plot(x,y). — ImportanceOfBeingErnest
– ImportanceOfBeingErnest, Commented Nov 7, 2018 at 17:25
To add to @ImportanceOfBeingErnest, since it's a recursive function it keep calculating from 1. It will be helpful if you have a global cache so you don't do a lot of repeating calculation. — Rocky Li
– Rocky Li, Commented Nov 7, 2018 at 17:33

Paul Rousseau · Accepted Answer · 2018-11-07 17:56:24Z

1

You could just add a list at the top:

import matplotlib as mpl
import matplotlib.pyplot as plt
changes_plot=[]
def pop(start_pop, years, percentage_change, max_pop):
    if years == 0:
         return start_pop
    else:
        changes = pop(start_pop,years-1,percentage_change,max_pop)
        changes_plot.append(changes)
        return changes + (1-changes/max_pop)*percentage_change*changes

pop(600,85,0.1,20000)
plt.plot(changes_plot)
plt.show()

answered Nov 7, 2018 at 17:56

Paul Rousseau

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1 Comment

Landon G Over a year ago

Thank you, this is what I was looking for!

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