Struct XBarRChart 

pub struct XBarRChart { /* private fields */ }

X-bar and Range (X-bar-R) control chart.

Monitors the process mean (X-bar chart) and process variability (R chart) using subgroup ranges. Suitable for subgroup sizes n = 2..=10.

Algorithm

1. For each subgroup, compute the mean (X-bar) and range (R).
2. Compute the grand mean (X-double-bar) and average range (R-bar).
3. X-bar chart limits: CL = X-double-bar, UCL/LCL = CL +/- A2 * R-bar.
4. R chart limits: CL = R-bar, UCL = D4 * R-bar, LCL = D3 * R-bar.

Examples

use u_analytics::spc::{XBarRChart, ControlChart};

let mut chart = XBarRChart::new(5);
chart.add_sample(&[25.0, 26.0, 24.5, 25.5, 25.0]);
chart.add_sample(&[25.2, 24.8, 25.1, 24.9, 25.3]);
chart.add_sample(&[25.1, 25.0, 24.7, 25.3, 24.9]);

let limits = chart.control_limits().expect("should have limits after 3 samples");
assert!(limits.ucl > limits.cl);
assert!(limits.cl > limits.lcl);

Reference

Montgomery, D.C. (2019). Introduction to Statistical Quality Control, 8th ed., Chapter 6: Control Charts for Variables.

Implementations

impl XBarRChart

pub fn new(subgroup_size: usize) -> Self

Create a new X-bar-R chart with the given subgroup size.

Panics

Panics if subgroup_size is not in the range 2..=10.

pub fn r_limits(&self) -> Option<ControlLimits>

Get the R chart control limits, or None if insufficient data.

pub fn r_points(&self) -> &[ChartPoint]

Get the R chart points.

Trait Implementations

impl ControlChart for XBarRChart

fn add_sample(&mut self, sample: &[f64])

Add a subgroup sample. The sample length must equal the chart’s subgroup size.

fn control_limits(&self) -> Option<ControlLimits>

Get the computed control limits, or None if insufficient data.

fn is_in_control(&self) -> bool

Check if the process is in statistical control.

fn violations(&self) -> Vec<Violation>

Get all violations detected across all chart points.

fn points(&self) -> &[ChartPoint]

Get all chart points.