Wc = gram(sys,'c') (gramian controllability)

In this command what is this 'c' stands for, how to specify c?

I am getting

??? Undefined function or variable 'c'.

after entering this gram command

Also can anybody tell me what size or dimension of this 'c' matrix?

if my state space system is

>>size(sys) State-space model with 46 outputs, 4 inputs, and 52 states.

Answer 1

[Rajiv Singh]

c is just a string indicating your choice of gramian type ('c' for controllability gramian and 'o' for observability)

Try: gram(sys, 'c')