getvariables

getvariables returns the internal index associated with an sdpvar variable

Syntax

k = getvariables(x)

sdpvar variables are built-up from internal variable indicies (i.e., the only internal name and reference is an integer).

yalmip('clear')
x = sdpvar(1);
getvariables(x)

ans = 
    1

y = sdpvar(2,3);
getvariables(y)
ans = 
    2 3 4 5 6 7 

Also nonlinear terms have internal indicies (and assosciated structures to explain how the term relates to other linear variables)

z = x^2;
getvariables(z)
ans = 
    8

Expressions are built up from variables

z = x + 3*x^2;
getvariables(z)
ans = 
    1 8

In most situations you typically use depends which returns the index to the involved linear variables.