symsum of matrix to extract element in the matrix

i want to sum this:

The code i used:

syms j

S=[0,1,0,0,0;1/2,0,1/2,0,0;0,1/2,0,1/2,0;0,0,1/2,0,1/2;0,0,0,1,0];

C1=symsum(S(1,j),j,1,5);

The code reterned me error. I want to do the polynomial summation as shwon above. l also would like to extract the element in matrix S for different j. Could you tell me what is the correct code i need to use? Thank you.

Answer 1

[Ameer Hamza]

Symbolic variables cannot be used as vector index. Also, your data is numeric, and it seems that you want to sum rows. Try this

S = [0,1,0,0,0;1/2,0,1/2,0,0;0,1/2,0,1/2,0;0,0,1/2,0,1/2;0,0,0,1,0];
C1 = sum(S, 2);

If you want to output in symbolic form

S = [0,1,0,0,0;1/2,0,1/2,0,0;0,1/2,0,1/2,0;0,0,1/2,0,1/2;0,0,0,1,0];
C1 = sum(sym(S), 2);

[Penglin Cai]

Thank you for the answer. But I do not want to sum the rows, l want to extract certain element in the matrix for different j. For example, i want to S11 for j=1, S12 for j=2.

[Ameer Hamza]

Try this

S = [0,1,0,0,0;1/2,0,1/2,0,0;0,1/2,0,1/2,0;0,0,1/2,0,1/2;0,0,0,1,0];
f = @(j) S(1, j);

Result

>> f(1) % j=1 => S11
ans =
     0
>> f(2) % j=2 => S12
ans =
     1