You can use max() to get the max value. The max function can also return the index of the maximum value in the vector. To get this, assign the result of the call to max to a two element vector instead of just a single variable.
e.g. z is your array,
>> [x, y] = max(z)
x =
7
y =
4
Here, 7 is the largest number at the 4th position(index).