min_avg_two_slice() {
    local -n _a="$1"
    local _idx=0
    local _min
    _min=$(echo "scale=10; (${_a[0]} + ${_a[1]}) / 2" | bc)
    local _count=${#_a[@]} _i
    for ((_i = 0; _i < _count - 1; _i++)); do
        local _cur
        _cur=$(echo "scale=10; (${_a[_i]} + ${_a[_i+1]}) / 2" | bc)
        if (( _i + 2 < _count )); then
            local _three
            _three=$(echo "scale=10; (${_a[_i]} + ${_a[_i+1]} + ${_a[_i+2]}) / 3" | bc)
            if (( $(echo "$_three < $_cur" | bc -l) )); then
                _cur=$_three
            fi
        fi
        if (( $(echo "$_cur < $_min" | bc -l) )); then
            _min=$_cur
            _idx=$_i
        fi
    done
    echo "$_idx"
}