Which of the functions are not performed by the Turing machine after reading a symbol?

The Turing machine performs three main functions after reading a symbol:

1. It writes a symbol: The Turing machine can write a symbol on the tape in the cell it is currently reading. This could be the same symbol it just read, a different symbol, or it could erase the symbol by writing a blank.

2. It moves the tape: The Turing machine can move the tape one cell to the left or to the right. This is how it changes which cell it is reading.

3. It changes state: The Turing machine can change its internal state. This is how it "remembers" what it has done and what it should do next.

So, any function that is not among these three is not performed by the Turing machine after reading a symbol. For example, it does not perform calculations or make decisions based on the symbol it just read. It simply follows the instructions given to it in its current state.