am using taylor series to process an audio signal.

this is the statement am using as taylor series

(x+h) == x + (h.*diff(x)) + (h^2.*diff(x,2))./factorial(2);

when i run the program it say matrix dimensions should match.

after degugging i realised that the first derivative is one less than the actual signal, second derivative is two less than the actual signal. how can I make these same size to sum them all. this is with respect to an audio signal.