Difficulty using "symsum" within a function definition

I'm trying to define a function "ansin" that takes in an array of test values and outputs the function values of the n-th degree Taylor polynomial for sin(x). I am totally unfamiliar with symsum and just tried to do the best I could to copy the notation in the MatLab documentation . Below is the summation that I'm trying to emulate, the code I used and the error I got.

The only difference between the formula and my code is that I've replaced all the n's with k's so that "n" can stand for the degree of taylor polynomial I want. Also I am not summing to infinity but to "n".

testcases = -2*pi + (4*pi).*rand(2000,1);
pred1 = ansin(testcases,1);
pred2 = ansin(testcases,2);
pred3 = ansin(testcases,3);
pred4 = ansin(testcases,4);

function y = ansin(x,n)

   y = symsum(((-1)^(k-1))*((x^(2*k-1))/factorial(2*k-1)), k, 1, n);

end

Undefined function or variable 'k'.

Error in Taylor_Polynomial_Practice>ansin (line 10) y = symsum(((-1)^(k-1))*((x^(2*k-1))/factorial(2*k-1)), k, 1, n);

Error in Taylor_Polynomial_Practice (line 2) pred1 = ansin(testcases,1);

[Riacon12]

I'd also like to add that I know there is taylor series functionality right in Matlab, but I'm using this example to get some experience with the symsum command.

Answer 1

[Walter Roberson]

This is correct. You do not have a definition for k.

syms k

[Riacon12]

Then I get the following:

Error using symengine Not a square matrix.

Error in sym/privBinaryOp (line 973) Csym = mupadmex(op,args{1}.s, args{2}.s, varargin{:});

Error in ^ (line 310) B = privBinaryOp(A, p, 'symobj::mpower');

Error in Taylor_Polynomial_Practice>ansin (line 9) y = symsum(((-1)^(k-1))*((x^(2*k-1))/factorial(2*k-1)), k, 1, n);

Error in Taylor_Polynomial_Practice (line 2) pred1 = ansin(testcases,1);

[Riacon12]

Nevermind, I needed to use ".^" instead of "^". Thank you for your help!