what does the following expression mean?

Question

I need to make a program to calculate the values of some variables, but i am stuck at this expression. I dont really understand the meaning of the last term (Xij).

I already tried searching on google, but i didn't find anything that could help me.

I just need to know how to evaluate that last term, Thanks.

Answer 1

A symbol with two indices often denotes the components of a matrix - you can think of it as a two dimensional array. From the equation it looks like $c_jx^j_i$ is a matrix multiplying a vector from the right.