GRASS Programmer's Manual
6.4.2(2012)
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00001 #include <math.h> 00002 #include <grass/imagery.h> 00003 /* sum: sum of x 00004 * sum2: sum of x squared 00005 * n: number of points 00006 */ 00007 00008 double I_variance(double sum, double sum2, int n) 00009 { 00010 if (n < 2) 00011 return ((double)0.0); 00012 else 00013 return ((sum2 - sum * sum / n) / (n - 1)); 00014 } 00015 00016 double I_stddev(double sum, double sum2, int n) 00017 { 00018 if (n < 2) 00019 return ((double)-99.0); 00020 else 00021 return sqrt(I_variance(sum, sum2, n)); 00022 }