# What is the difference between 'x' and 'plus' symbol in the block diagram

Generally speaking, what is the difference between the 'x' and the 'plus' symbol in a closed loop block diagram?

For example, in (https://ieeexplore.ieee.org/document/6983570)

, what's the difference between the 'cross' sign and the 'plus' sign?

• The same as between + and x operators in math (note though that multiplication in Laplace domain is a convolution in time domain). – Eugene Sh. Mar 20 '19 at 15:52

The 'x' symbol you show refers to multiplication, its output is $$\B\delta\$$.
The '+' symbol you show refers to addition, the one on the left outputs $$\P^*-P\$$.