// SPDX-License-Identifier: MIT
// Copyright (c) 2026 Incoprea
// Measure paired linear association
// Not compiled or tested in-world
// Setup: Place in a spare owned prim. Set DATA as x/y pairs with at least two observations. Touch to run; output is private to the owner.
// Stop / restore: Disable/remove. No scene changes or external calls.
// Notes: Correlation describes linear association and does not establish causation. Constant input series are rejected.
// License: see LICENSE in this distribution.
// Original Incoprea. MIT.
list DATA=[1.0,2.0,2.0,3.0,3.0,5.0,4.0,4.0];
default
{
    touch_start(integer detectedCount)
    {
        if(llDetectedKey(0)!=llGetOwner())return;
        integer length=llGetListLength(DATA);
        if(length<4||length%2)
        {
            llOwnerSay("Need two or more pairs.");
            return;
        }
        float count=(float)(length/2);
        float mx;
        float my;
        integer i;
        for(i=0;i<length;i+=2)
        {
            mx+=llList2Float(DATA,i);
            my+=llList2Float(DATA,i+1);
        }
        mx/=count;
        my/=count;
        float xx;
        float yy;
        float xy;
        for(i=0;i<length;i+=2)
        {
            float x=llList2Float(DATA,i)-mx;
            float y=llList2Float(DATA,i+1)-my;
            xx+=x*x;
            yy+=y*y;
            xy+=x*y;
        }
        if(xx<0.000001||yy<0.000001)
        {
            llOwnerSay("Constant or nearly constant series.");
            return;
        }
        llOwnerSay("Correlation="+(string)(xy/llSqrt(xx*yy)));
    }
}