Your matlab code could be as follows
s = serial('COM8','BaudRate',9600); %creates a serial object
flushinput(s) %this discards all previous s values
fopen(s);
fwrite(s,255); % allows you to send a single int here, I'm sending 255
This should be paired with a read method, in your arduino IDE. Make sure that you type in the correct COM port and baud rate. Baud rate should be the same (in your serial object as well as the arduino).
