Python中的函数求和

Question

I'm new to Python programming. Coming from a MATLAB background. I'm looking something similar to symsum function from MATLAB in Python.

I have my array,

a = np.linspace([0,3.14])

I want to sum

sin(2*i*a) where i ranges from 1 to 20

and then plot the results between a and y

I tried the following

y = nsum(lambda i: np.sin(2*i*a), [0,20])

I'm stuck at this point.

Edit. The MATLAB equivalent would be

a = linspace(0,pi) syms iy=double(symsum(sin(2*i*a),i,0,20)

Answer 1

edit

Looks like symsum is part of a symbolics package (in MATLAB and Octave). sympy is the Python symbolics package. Its integration with numpy is looser.

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Here's a guess as to what you are trying to do:

A range of a values:

In [180]: a = np.linspace(0, np.pi, 100)                                                     

Outer product with (0,1,2,3,4) (uses broadcasting)

In [181]: x = np.arange(5)[:,None]*a          

Sum the sin values, and plot:

In [182]: y = np.sin(2*x).sum(axis=0)                                                        
In [184]: plt.plot(a,y)