# Exercise 12

## Mean of a vector

If we have a vector $$X$$ containing $$n$$ values, then the mean $$\bar{X}$$ is:

$$\bar{X} = \frac{1}{n} \sum_{i=1}^{N} \left( X_{i} \right)$$

In MATLAB, Python (NumPy) and R there are built-in functions for computing the mean of a vector. Conveniently, in all three languages the function is called mean().

In MATLAB:

x = [2,1,5,4,8,3,4,3];
mean(x)

ans =

3.7500


In Python / NumPy: (started using ipython --pylab)

x = array([2,1,5,4,8,3,4,3], 'float')
mean(x)
Out[2]: 3.75


In R:

x <- c(2,1,5,4,8,3,4,3)
mean(x)
[1] 3.75


## from scratch

Write a function called mymean() that computes the mean of a list of numbers. Do it from scratch, in other words don't use the built-in function mean().

Paul Gribble | fall 2014