How to add markers at certain x coordinates using Sympy plot

Question

I have a Sympy function, a sequence of x coordinates and a graph drawn using "plot".

import numpy as np
import sympy as sp

x = sp.Symbol('x')
xs = np.linspace(-2, 3, 5) #[-2.   -0.75  0.5   1.75  3.  ]
ys = sp.cos(2*x)*(sp.sin(2*x) + 1.5)+sp.cos(x)
graph = sp.plot(ys, xlim=[-2,3])

How could I draw markers on the function at X coordinates from xs variable?

The graph I get:

The graph I would like to get:

To get the corresponding y-coordinates: [ys.subs(x, xi).evalf() for xi in xs] — JohanC
– JohanC, Commented Nov 26, 2021 at 19:47

JohanC · Accepted Answer · 2022-03-15 09:16:25Z

1

Sympy's plot supports a markers= keyword. This is a list of dictionaries towards matplotlib's plot. Sympy's subs can be used to fill in an x value into the formula.

import numpy as np
import sympy as sp

x = sp.Symbol('x')
y = sp.Symbol('y')
ys = sp.cos(2 * x) * (sp.sin(2 * x) + 1.5) + sp.cos(x)

xs = np.linspace(-2, 3, 5)  # [-2.   -0.75  0.5   1.75  3.  ]
yvals = [ys.subs(x, xi) for xi in xs]

plot = sp.plot(ys, xlim=[-2.2, 3.2],
               markers=[{'args': [xs, yvals, 'ro']}])

edited Mar 15, 2022 at 9:16

answered Nov 26, 2021 at 20:03

JohanC

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