I’m writing a python function to draw a simple rectangle, the vertex points are parameters. Well, this does not work correctly and I can’t seem to find out why its plotting all over the place. EDIT: as for my imports. So sp is sympy. As for the expected result to draw a rectangle of course.

%matplotlib inline import sympy as sp import numpy as np import matplotlib.pyplot as plt import math def draw_rectangle(P1,P2,P3,P4): p1, p2, p3, p4 = sp.Point(P1[0], P1[1]), sp.Point(P2[0], P2[1]), sp.Point(P3[0], P3[1]), sp.Point(P4[0], P4[1]) plt.plot(p1,p2) plt.plot(p2,p3) plt.plot(p3,p4) plt.plot(p4,p1) P1=[20,30] P2=[40,30] P3=[40,60] P4=[20,60] draw_rectangle(P1,P2,P3,P4)

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## Answer

The delivery of the x-y coordinates is mixed up in your code. `p1`

is still in the same form as `P1`

, i.e., an x-y pair. But matplotlib `plt.plot()`

expects a list of x-values followed by a list of y-values. Hence, this misunderstanding – matplotlib interpreted in `plt.plot(p1,p2)`

`p1`

as two x-values and `p2`

as two y-values. So, we have to chain the x- and the y-values together before plotting.

import sympy as sp import matplotlib.pyplot as plt def draw_rectangle(P1,P2,P3,P4): p1, p2 = sp.Point(P1[0], P1[1]), sp.Point(P2[0], P2[1]) p3, p4 = sp.Point(P3[0], P3[1]), sp.Point(P4[0], P4[1]) plt.plot(*zip(p1,p2)) plt.plot(*zip(p2,p3)) plt.plot(*zip(p3,p4)) plt.plot(*zip(p4,p1)) #or alternatively #plt.plot(*zip(p1, p2, p3, p4, p1)) P1=[20,30] P2=[40,30] P3=[40,60] P4=[20,60] draw_rectangle(P1,P2,P3,P4) plt.show()

Sample output:

However, it remains unclear why you converted your data into `sympy`

points before plotting. You could have directly used `P1`

, `P2`

,…, but maybe this is required for some other program parts we are not aware of. Or you actually wanted to use another `sympy`

function, not `sp.point`

, but I don’t speak fluent `sympy`

, so cannot comment on that.