# Moves in a Turing Machine

In a Turing Machine i understand that δ(q,x) is a transition function that results in a Change in ID. What does δ(q, Xj) =(P, y, L) mean.I understand that L stands for move left.Is P the new state and y the symbol at the tape head?Is it right?

The input string to be processed is X1X2 ... Xn, and the present symbol under the R/W head is Xi So the ID before processing Xi is

Before processing i understand that q is the current state and since the TM moves left the current state become p.What is y?

Yep, you're right. $y$ is the symbol that was written when the tape head moved. So the statement
$$\delta(q, x_j) = (p, y, L)$$
should be read as "in state $q$, upon reading symbol $x_j$, write a $y$ on the tape, transition to state $p$, and move left".
• From the picture you posted it looks like that's correct. The $y$ is written where the read-write head of the machine was, at position $x_i$. – Eli Rose Nov 27 '15 at 6:09