STDEV Function

Standard Library function that computes the standard deviation and (optionally) the mean of the input array.

result = STDEV(array [, mean])

array The array to be processed. Can be of any data type except string.

mean (optional) The mean of array.

result The standard deviation of array. If the Dimension keyword is used, then the value of result and mean will each have the structure of the input array, but with dimension n collapsed.

Dimension An integer (n 0) indicates that the standard deviation is to be computed over dimension n of the input array.

Variance If nonzero, the variance of array is returned instead of the standard deviation.

Mean, standard deviation and variance are basic statistical tools used in a variety of applications. They are computed as follows:

where n is the number of elements in array.

These equations are implemented as follows:

mean = TOTAL(array) / N_ELEMENTS(array)
std = SQRT(TOTAL((array - mean)^2) / (N_ELEMENTS(array) - 1))

The variance is implemented as follows:

variance = TOTAL((array - mean)^2) / (N_ELEMENTS(array) - 1) 

y = [1, 5, 9, 3, 10, 4]

; Create a simple array.

std = STDEV(y, arrmean)

; Compute the standard deviation and mean array value.

PRINT, std, arrmean

3.50238    5.33333

; Print the results.

AVG, SIGMA