Array in a symsum

Hello! I want to implement a formula such F(k)=k*symsum(x(n)*n,n,1,8). There is my code, but i don't know how to put vector x(n) in that sum. It doesn t work.

x=[1 3 5 4]

syms x k n

F(k)=k*symsum(x(n)*n,n,1,4)

That s my code. I want to do>>>>>>>>>>> F(k)=k*[x(1)*1+x(2)*2 +x(3)*3....], but i want the valueof x(1) and x(2)...

So the result may be>>>>>>>>>>>> F(k)=k*[1*1+3*2+5*3+4*4]

Answer 1

[Walter Roberson]

You are attempting to index x with a symbolic variable. That is not possible with MATLAB, and that is something that is not expected to change any time soon.

Construct the definite terms instead

nx = x(:)*(1:length(x));
F(k) = k*nx;

Note that the first line is algebraic matrix multiplication * operator, column * row giving scalar result

[Mihai Iustinian]

Ok, but if x=sin(2*pi*1/32*(0:127))? It is a sinusoidal signal with 4 period, represented on 128 point.

How do I construct x now?

[Walter Roberson]

syms k
n = 1:128;
Pi = sym(pi);
x = sin(2*Pi*1/32*(n-1));
nx = simplify(n * x(:))

nx = 

F(k) = k*nx

F(k) = 

[Mihai Iustinian]

Thanks!!!