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Merged
dm61 merged 1 commit into from
Oct 23, 2018
Merged

IRC class in a separate file, with comments #9

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4 changes: 4 additions & 0 deletions Loop.xcodeproj/project.pbxproj
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Expand Down Expand Up @@ -1195,6 +1197,7 @@
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4F70C20F1DE8FAC5006380B7 /* StatusExtensionDataManager.swift */,
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430B29932041F5B300BA9F93 /* UserDefaults+Loop.swift in Sources */,
4341F4EB1EDB92AC001C936B /* LogglyService.swift in Sources */,
43CE7CDE1CA8B63E003CC1B0 /* Data.swift in Sources */,
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161 changes: 161 additions & 0 deletions Loop/Managers/IntegralRetrospectiveCorrection.swift
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//
// IntegralRetrospectiveCorrection.swift
// Loop
//
// Created by Dragan Maksimovic on 10/21/18.
// Copyright © 2018 LoopKit Authors. All rights reserved.
//

import Foundation
import HealthKit
import LoopKit

/**
Integral Retrospective Correction (IRC) calculates a correction effect in glucose prediction based on a timeline of past discrepancies between observed glucose movement and movement expected based on insulin and carb models. Integral retrospective correction acts as a proportional-integral-differential (PID) controller aimed at reducing modeling errors in glucose prediction.

In the above summary, "discrepancy" is a difference between the actual glucose and the model predicted glucose over retrospective correction grouping interval (set to 30 min in LoopSettings), whereas "past discrepancies" refers to a timeline of discrepancies computed over retrospective correction integration interval (set to 180 min in Loop Settings).

*/
class IntegralRetrospectiveCorrection {

/**
Integral retrospective correction parameters:
- currentDiscrepancyGain: Standard retrospective correction gain
- persistentDiscrepancyGain: Gain for persistent long-term modeling errors, must be greater than or equal to currentDiscrepancyGain
- correctionTimeConstant: How fast integral effect accumulates in response to persistent errors
- delta: Glucose sampling time interval (5 min)
- differentialGain: Differential effect gain
- maximumCorrectionEffectDuration: Maximum duration of the correction effect in glucose prediction
*/
static let currentDiscrepancyGain: Double = 1.0
static let persistentDiscrepancyGain: Double = 5.0
static let correctionTimeConstant: TimeInterval = TimeInterval(minutes: 120.0)
static let differentialGain: Double = 2.0
static let delta: TimeInterval = TimeInterval(minutes: 5.0)
static let maximumCorrectionEffectDuration: TimeInterval = TimeInterval(minutes: 240.0)

/// Initialize computed integral retrospective correction parameters
static let integralForget: Double = exp( -delta.minutes / correctionTimeConstant.minutes )
static let integralGain: Double = ((1 - integralForget) / integralForget) *
(persistentDiscrepancyGain - currentDiscrepancyGain)
static let proportionalGain: Double = currentDiscrepancyGain - integralGain

/// All math is performed with glucose expressed in mg/dL
private let unit = HKUnit.milligramsPerDeciliter

/// Effect duration for standard retrospective correction
private let effectDuration: TimeInterval

/// Settings relevant for calculation of effect limits
private let settings: LoopSettings
private let correctionRange: GlucoseRangeSchedule
private let insulinSensitivity: InsulinSensitivitySchedule
private let basalRates: BasalRateSchedule

/**
Initialize integral retrospective correction settings based on current values of user settings

- Parameters:
- effectDuration: Effect duration for standard retrospective correction
- settings: User Loop settings
- correctionRange: User correction range settings
- insulinSensitivity: User insulin sensitivity schedule
- basalRates: User basal rate schedule

- Returns: Integral Retrospective Correction customized with controller parameters and user settings
*/
init(_ effectDuration: TimeInterval, _ settings: LoopSettings, _ correctionRange: GlucoseRangeSchedule, _ insulinSensitivity: InsulinSensitivitySchedule, _ basalRates: BasalRateSchedule) {

self.effectDuration = effectDuration
self.settings = settings
self.correctionRange = correctionRange
self.insulinSensitivity = insulinSensitivity
self.basalRates = basalRates
}

/**
Calculate correction effect and correction effect duration based on timeline of past discrepancies

- Parameters:
- currentDate: Date when timeline of past discrepancies is computed
- currentDiscrepancy: Most recent discrepancy
- latestGlucose: Most recent glucose
- pastDiscrepancies: Timeline of past discepancies

- Returns:
- totalRetrospectiveCorrection: Overall glucose effect
- integralCorrectionEffectDuration: Effect duration

*/
func updateIntegralRetrospectiveCorrection(_ currentDate: Date,
_ currentDiscrepancy: GlucoseChange, _ latestGlucose: GlucoseValue,
_ pastDiscrepancies: [GlucoseChange]) -> (HKQuantity, TimeInterval) {

/// To reduce response delay, integral retrospective correction is computed over an array of recent contiguous discrepancy values having the same sign as the most recent discrepancy value
var recentDiscrepancyValues: [Double] = []
var nextDiscrepancy = currentDiscrepancy
let currentDiscrepancySign = currentDiscrepancy.quantity.doubleValue(for: unit).sign
for pastDiscrepancy in pastDiscrepancies.reversed() {
let pastDiscrepancyValue = pastDiscrepancy.quantity.doubleValue(for: unit)
if (pastDiscrepancyValue.sign == currentDiscrepancySign &&
nextDiscrepancy.endDate.timeIntervalSince(pastDiscrepancy.endDate)
<= settings.recencyInterval &&
abs(pastDiscrepancyValue) >= 0.1)
{
recentDiscrepancyValues.append(pastDiscrepancyValue)
nextDiscrepancy = pastDiscrepancy
} else {
break
}
}
recentDiscrepancyValues = recentDiscrepancyValues.reversed()

/// User settings relevant for calculations of effect limits
let currentSensitivity = insulinSensitivity.quantity(at: currentDate).doubleValue(for: unit)
let currentBasalRate = basalRates.value(at: currentDate)
let correctionRangeMin = correctionRange.minQuantity(at: currentDate).doubleValue(for: unit)
let correctionRangeMax = correctionRange.maxQuantity(at: currentDate).doubleValue(for: unit)

let latestGlucoseValue = latestGlucose.quantity.doubleValue(for: unit) // most recent glucose

/// Safety limit for (+) integral effect. The limit is set to a larger value if the current blood glucose is further away from the correction range because we have more time available for corrections
let glucoseError = latestGlucoseValue - correctionRangeMax
let zeroTempEffect = abs(currentSensitivity * currentBasalRate)
let integralEffectPositiveLimit = min(max(glucoseError, 0.5 * zeroTempEffect), 4.0 * zeroTempEffect)

/// Limit for (-) integral effect: glucose prediction reduced by no more than 10 mg/dL below the correction range minimum
let integralEffectNegativeLimit = -max(10.0, latestGlucoseValue - correctionRangeMin)

/// Integral correction math
var integralCorrection = 0.0
var integralCorrectionEffectMinutes = effectDuration.minutes - 2.0 * IntegralRetrospectiveCorrection.delta.minutes
for discrepancy in recentDiscrepancyValues {
integralCorrection =
IntegralRetrospectiveCorrection.integralForget * integralCorrection +
IntegralRetrospectiveCorrection.integralGain * discrepancy
integralCorrectionEffectMinutes += 2.0 * IntegralRetrospectiveCorrection.delta.minutes
}
/// Limits applied to integral correction effect and effect duration
integralCorrection = min(max(integralCorrection, integralEffectNegativeLimit), integralEffectPositiveLimit)
integralCorrectionEffectMinutes = min(integralCorrectionEffectMinutes, IntegralRetrospectiveCorrection.maximumCorrectionEffectDuration.minutes)

/// Differential correction math
let currentDiscrepancyValue = currentDiscrepancy.quantity.doubleValue(for: unit)
var differentialDiscrepancy: Double = 0.0
if recentDiscrepancyValues.count > 1 {
let previousDiscrepancyValue = recentDiscrepancyValues[recentDiscrepancyValues.count - 2]
differentialDiscrepancy = currentDiscrepancyValue - previousDiscrepancyValue
}

/// Overall glucose effect calculated as a sum of propotional, integral and differential correction effects
let proportionalCorrection = IntegralRetrospectiveCorrection.proportionalGain * currentDiscrepancyValue
let differentialCorrection = IntegralRetrospectiveCorrection.differentialGain * differentialDiscrepancy
let totalCorrection = proportionalCorrection + integralCorrection + differentialCorrection
let totalRetrospectiveCorrection = HKQuantity(unit: unit, doubleValue: totalCorrection)
let integralCorrectionEffectDuration = TimeInterval(minutes: integralCorrectionEffectMinutes)

/// Return overall retrospective correction effect and effect duration
return((totalRetrospectiveCorrection, integralCorrectionEffectDuration))
}

}
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