Write a user written function that expects as its input argument a

vector of x values and a vector of corresponding y$-$values. The function must return a matrix

with $2$ columns. The first column must contain x values. The second column must contain the

centered difference approximations for the second derivative d$2$y$/$dx$2$ at the given x values. In

other words, the x values $[$x$2,$ x$3,...,$ xn$-1]$ and corresponding second derivatives should be

returned. If the x$-$spacing is not uniform, the function must return an error.