find the array position of an entry closest to some arbitrary value

a friend asked:

matlab question: i have an array of data. how do i get matlab to find the position of an entry closest to some arbitrary value?
for instance, i would have
a= [1; 4; 6; 8; 12]
i want to search for 9 and have matlab spit back 4, the entry in a closest to 9.

here's one way to solve that problem (assuming that variable k=9):

>> [trash array_position] = min(abs(a - k))

wheree array_position is the desired index value.