EV3 Wired Brick to Brick communication
The reading you have done about connecting input port 4 is for the NXT, not the EV3. The NXT has a special feature on that port for RS485 serial communications. This is not present on the EV3 bricks.

The EV3 bricks are designed to be able to be daisy chained via USB. There are "Message" blocks in the EV3 software for sending messages from brick to brick. I'm not sure about LabView and Matlab, but I suspect that have a similar block/function for sending messages.