GRASS Programmer's Manual
6.4.3(2013)-r
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var.c
Go to the documentation of this file.
1
#include <math.h>
2
#include <grass/imagery.h>
3
/* sum: sum of x
4
* sum2: sum of x squared
5
* n: number of points
6
*/
7
8
double
I_variance
(
double
sum,
double
sum2,
int
n)
9
{
10
if
(n < 2)
11
return
((
double
)0.0);
12
else
13
return
((sum2 - sum * sum / n) / (n - 1));
14
}
15
16
double
I_stddev
(
double
sum,
double
sum2,
int
n)
17
{
18
if
(n < 2)
19
return
((
double
)-99.0);
20
else
21
return
sqrt(
I_variance
(sum, sum2, n));
22
}
lib
imagery
var.c
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