from sympy.solvers import solve
from sympy import Symbol
from sympy import solve, Poly, Eq, Function, exp
from sympy.abc import x, y, z, a, b
import matplotlib.pyplot as plt
import numpy as np

def coef0(k0,c,N):
    return k0**2*c**2*N**2
def coef1(k0,q,a):
    return -(k0**2+q**2+0.25*a**2)
def coef2(k0):
    return 1
def sols(a0,a1,a2):
    omg2=Symbol('omg2')
    c=solve(Poly(a2*omg2**2+a1*omg2+a0),omg2)
    return c

N=10
a=20.42
k0=np.arange(1,500,1)
n=np.arange(1,11,1)
x=k0
c=1

plt.figure(1)

plt.rc('text', usetex=True)
plt.rc('font', family='serif')

for i in n:
    q=i*np.pi
    c0=coef0(k0,c,N)
    c1=coef1(k0,qq,a)
    c2=coef2(k0)
    y1,y2=sols(c0,c1,c2)
    plt.plot(x,y1,'b',x,y2,'r')

plt.xlabel(r'$\bar{k}^{2}_{0}$',fontsize=16)
plt.ylabel(r'$\bar{\omega}^{2}$',fontsize=16)
plt.title(r"Arithmetic Dispersion Diagram",
          fontsize=16, color='purple')
plt.legend([r'$\bar{\omega}_{p}$',r'$\bar{\omega}_{g}$'])

plt.ylim(1,500)
plt.xlim(1,30)
plt.show()

(Nov-13-2018, 12:54 PM)pianistseb Wrote: I have always the same error.