Remezアルゴリズムを様々な関数でテストしたいです。

前提・実現したいこと

remezアルゴリズムをpythonで表していますが、f(x)=sin(x)以外にもcos(x)やtan(x)など、他の関数もテストしたいです

発生している問題・エラーメッセージ

リストを使ったのですが、多分そのせいでこのエラーが出ます。他の方法でやるしかないのでしょうか？
The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

該当のソースコード

Python
1def f(x):
2    return np.sin(x)
3lower=-np.pi
4upper=np.pi
5n=4
6reference_points=list(np.linspace(lower,upper,n+2))
7
8
9
10class BestApprox:
11    tol=1.e-12
12    max_iter=100
13    a=[]
14    error_absolute_h=[]
15    def __init__(self,function):
16        self.f=function
17    def remez(self,reference=None):
18        self.name_dict={'lower':'lower bound','upper':'upper bound','n':'degree of polynomial'}
19        self.var_dict={'lower':None,'upper':None,'n':None}
20        if reference!=None: 
21            if not isinstance(reference,list):
22                print("Oops! Initial guess not of 'list' data type.")
23                return
24            else:
25                self.reference=reference
26                self.var_dict['lower']=min(self.reference)
27                self.var_dict['upper']=max(self.reference)
28                self.n=len(self.reference)-2
29        elif reference==None: correct input
30            for i in self.var_dict:
31                while True:
32                    try:
33                        self.var_dict[str(i)]=float(input(f'Please specify {self.name_dict[str(i)]}: '))
34                    except ValueError:
35                        print('Oops! Input non-numeric! Try again')
36                    else:
37                        break
38            self.n=int(self.var_dict['n']) # for better readability, n will also be stored as attribute instead of dict.
39            self.reference=list(np.linspace(self.var_dict['lower'],self.var_dict['upper'],self.n+2))
40
41        error_absolute_h=[]
42        for i in range(self.max_iter):
43            Y=np.array([self.f(i) for i in self.reference])
44            M=np.zeros((self.n+2)**2).reshape(self.n+2,self.n+2)
45        
46            for i in range(self.n+2):
47                M[i,0]=1
48                M[i,-1]=(-1)**i 
49            for i in range(self.n+2):
50                for j in range(1,self.n+1):
51                    M[i,j]=(self.reference[i])**j
52               
53            X=sp.solve(M,Y)
54            
55            error_absolute_h.append(abs(X[-1])) 
56            
57            def p(x):
58                return sum(X[i]*x**i for i in range(self.n+1))
59            
60            error=([abs(f(x)-p(x)) for x in np.linspace(self.var_dict['lower'],self.var_dict['upper'],100)])
61            max_error=max(error)
62            if max_error-abs(X[-1])<self.tol:
63                
64                np.set_printoptions(precision=4)
65                print(f'convergense observed after {i+1} iterations, the coefficients of the polynomial that is the best approx of f are:{X[:-1]}')
66                
67                print([(p(self.reference[i])-self.f(self.reference[i])) for i in range(len(self.reference))])
68                print(error_absolute_h)
69                
70                self.a=X[:-1]
71                break
72            index=error.index(max_error)
73            interval=list(np.linspace(self.var_dict['lower'],self.var_dict['upper'],100))
74            eta=interval[index]
75            self.reference.append(eta)
76            self.reference.sort()
77            
78            
79            if self.reference[0]<=eta<=self.reference[-1]:
80                if ((self.f(eta)-p(eta))/(self.f(self.reference[self.reference.index(eta)-1])-p(self.reference[self.reference.index(eta)-1])))>0:
81                    self.reference.remove(self.reference[self.reference.index(eta)-1])
82                else:
83                    self.reference.remove(self.reference[self.reference.index(eta)+1])
84            elif eta<self.reference[0]:
85                if ((self.f(eta)-p(eta))/(self.f(self.reference[0])-p(self.reference[0]))):
86                    self.reference.remove(self.reference[0])
87                else:
88                    self.reference.remove(self.reference[-1])
89            elif eta>self.reference[-1]:
90                if ((self.f(eta)-p(eta))/(self.f(self.reference[-1])-p(self.reference[-1]))):
91                    self.reference.remove(self.reference[-1])
92                else:
93                    self.reference.remove(self.reference[0])
94            self.reference.sort()
95            Y[self.reference.index(eta)]=self.f(eta)
96            for i in range(1,self.n+1):
97                M[self.reference.index(eta),i]=(self.reference[self.reference.index(eta)])**i
98                
99        
100    def plot_f_remez(self):
101        x=np.linspace(self.var_dict['lower'],self.var_dict['upper'],100)
102        plt.plot(x,self.f(x)[0],'r',x,sum(self.a[i]*(x**i) for i in range(self.n+1)),'k:')
103        plt.show()
104 
105
106def f(x):#テスト用にf(x)を再定義
107    func=[np.sin(x),np.cos(x),np.tan(x)]#このリストの中の関数でテストしたい
108    message="result with fx={func} is {result}."
109    for n in func:
110        return func
111    A=f(x)
112    print(message.format(fx=func,result=A))
113    
114lower=-np.pi
115upper=np.pi
116n=4
117reference_points=list(np.linspace(lower,upper,n+2))
118
119x=np.linspace(lower,upper,100)
120message="result with x={x} is {result}."
121
122print(f(x)[0])
123sin=BestApprox(f)
124sin.remez(reference_points)
125sin.plot_f_remez()