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docs/ai/Common/DTS.Common.Calculations.md

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+---
+source_files:
+  - Common/DTS.Common.Calculations/ChannelData.cs
+  - Common/DTS.Common.Calculations/Integral.cs
+  - Common/DTS.Common.Calculations/Resultant.cs
+  - Common/DTS.Common.Calculations/HeadInjuryCriterion.cs
+generated_at: "2026-04-17T16:03:17.838159+00:00"
+model: "zai-org/GLM-5-FP8"
+schema_version: 1
+sha256: "f8b0959de0ed6cde"
+---
+
+# DTS.Common.Calculations
+
+### Purpose
+This module provides mathematical calculation utilities for signal processing and injury analysis. It supports integration of time-series data, generation of resultant vectors from multi-axis inputs, and computation of the Head Injury Criterion (HIC) used in impact analysis. The module is designed to work with filtered engineering unit data from sensor channels.
+
+### Public Interface
+
+**ChannelData**
+- `string Units { get; }` - Engineering units of the data (read-only, set via constructor).
+- `double[] FilteredEU { get; set; }` - Pre-filtered engineering unit data array.
+- `ChannelData(string units)` - Constructor accepting engineering units string.
+
+**Integral** (static class)
+- `static double DefiniteIntegral(double[] input, int start, int end, double SPS)` - Computes definite integral using trapezoidal summation. Parameters: input data array, start index (inclusive), end index (inclusive), samples per second. Returns integrated value.
+
+**Resultant** (static class)
+- `static ChannelData GenerateResultantChannel(List<ChannelData> channels)` - Generates a resultant vector channel from input channels using sum-of-squares method. Returns new `ChannelData` with sqrt(Σxi²) values. Asserts all channels have same length and units.
+
+**HeadInjuryCriterion**
+- `static HICResult GetHeadInjuryCriterion(ChannelData resultant, double SPS, int clipLengthMS)` - Calculates maximum HIC over the input data for the specified clip length. Returns `HICResult` with max HIC value and sample indices.
+- **HICResult** (nested class)
+  - `int StartSample { get; }` - Start sample index of max HIC window.
+  - `int EndSample { get; }` - End sample index of max HIC window.
+  - `int HicLengthMS { get; }` - HIC window length in milliseconds.
+  - `double HIC { get; }` - The HIC value.
+  - `HICResult(double hic, int hicLength, int startSample, int endSample)` - Constructor.
+
+### Invariants
+- `DefiniteIntegral` assumes input data is tightly time-aligned (uniform sampling interval).
+- `GenerateResultantChannel` asserts all input channels have identical `FilteredEU.Length` and identical `Units`.
+- `GetHeadInjuryCriterion` requires `SPS > 0` and `clipLengthMS > 0` (asserted).
+- `GetHeadInjuryCriterion` asserts data length is at least `clipLengthMS` worth of samples.
+- HIC calculation uses the formula: `hic = clipInSeconds * (integral / clipInSeconds)^2.5`
+
+### Dependencies
+- **Depends on**: `System`, `System.Collections.Generic`, `System.Linq`
+- **Depended on by**: Unc