This is an algebraic loop, which means that the output of the block depends directly on the input.
In this case, y cannot be computed without knowledge of u -- both of which refer to the same signal. As the error messages say, this is not valid.
If it makes sense given your modeling requirements, I would recommend using a Unit Delay block in the loop. This delay will change the equations from:
y = u (AT THE CURRENT TIME STEP) + randn(1,2); % Does not work
to:
y = u (AT THE PREVIOUS TIME STEP) + randn(1,2); % Will work
Just make sure the Unit Delay block is sampled at the rate you want by setting its sample time parameter.
- Sebastian
