LIST STAT STD DEV

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/LSL

LIST_STAT_STD_DEV

Description

Constant: integer LIST_STAT_STD_DEV = 5;

The integer constant LIST_STAT_STD_DEV has the value 5

Calculates the sample standard deviation of a list of numbers.

float sample_standard_deviation = llListStatistics( LIST_STAT_STD_DEV, numList );

Standard deviation is a measure of how spread out the values are, and is defined as the square root of the average of the squares of the numbers:

integer count = (integer)llListStatistics( LIST_STAT_NUM_COUNT, numList );
float standard_deviation = llSqrt( llListStatistics( LIST_STAT_SUM_SQUARES , numList ) ) / count;

The sample standard deviation is used when the list doesn't (or can't) include the entire set of numbers, like the mass of every prim in SL. The true standard deviation is therefore estimated by using the sample standard deviation, which is defined by,

integer count = (integer)llListStatistics( LIST_STAT_NUM_COUNT, numList );
float sample_standard_deviation = llSqrt( llListStatistics( LIST_STAT_SUM_SQUARES , numList ) ) / (count - 1);

Another way to calculate the sample standard deviation is

    list numList = [1,1,1,2,1000,1000,1000];
    integer count = llGetListLength( numList );
    float sum = 0;
    float mean = llListStatistics( LIST_STAT_MEAN, numList );
    integer i = 0;
    for (; i<count; ++i) {
        float val = llList2Float( numList, i );
        float diff = val - mean;
        sum += ( diff * diff );
    }
    float sample_stdev = llSqrt( sum / (count - 1) ); 
    float true_stdev = llSqrt( sum / count ); 
    llOwnerSay((string)true_stdev);
    llOwnerSay((string)sample_stdev);
    llOwnerSay((string)llListStatistics( LIST_STAT_STD_DEV, numList ));
}

Caveats

Related Articles

Functions

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llListStatistics

Deep Notes

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Signature
integer LIST_STAT_STD_DEV = 5;