Mass Index
Install and import#
npm install fintech-algorithmsimport { massIndex } from "fintech-algorithms/technical-indicators/trend-systems/mass-index";Signature#
massIndex(input)Takes the ratio of a 9-period EMA of the high-low range to the 9-period EMA of that EMA, then sums the ratio over a longer window, so range expansion after a contraction pushes the total up.
Parameters#
| Name | Type | Notes |
|---|---|---|
input | TopicInput | bars is the OHLCV series, validated for finite prices, strictly increasing timestamp, a single adjustment basis, non-negative volume, and a high and low that bracket the other prices. From parameters this topic reads sum_period (integer, minimum 2, default 25), the length of the final sum; the two EMA lengths are fixed at 9 and are not configurable. period is still validated by the family, with the same integer-minimum-2 rule, but no branch of this calculation uses it. |
Returns#
TopicResult
series and latest carry a single value key. The chained EMAs make the warm-up much longer than sum_period alone suggests.
Warm-up#
The first sum_period + 15 bars (40 by default) positions are null. The first EMA resolves at index 8, the EMA of that EMA at index 16, and the sum then needs sum_period consecutive ratios. With the default sum_period of 25 the first value lands at index 40, so ready_at is 40.
Errors#
- When
parameters.sum_periodorparameters.periodis present but is not an integer of at least 2 — throws Error - When
barsis empty, or a bar has a non-finite price, a negative volume, a timestamp not greater than the previous one, or a high below its open, low, or close — throws Error
Complexity: time O(n * sum_period),
space O(n).
Worked example#
executed Captured by running this function on the input its own test provides. Real output of real code — but not asserted against a published figure.
Input#
{
"bars": [
{
"timestamp": "2024-01-02",
"basis": "synthetic-unadjusted",
"open": 100,
"high": 101.45,
"low": 98.695,
"close": 100,
"volume": 750000,
"benchmark": 200
},
{
"timestamp": "2024-01-03",
"basis": "synthetic-unadjusted",
"open": 101.49111452,
"high": 103.38381693,
"low": 100.05480022,
"close": 101.78791214,
"volume": 795117,
"benchmark": 200.56326135
},
{
"timestamp": "2024-01-04",
"basis": "synthetic-unadjusted",
"open": 102.45519048,
"high": 104.6701838,
"low": 100.91147007,
"close": 102.9549389,
"volume": 840234,
"benchmark": 201.11020913
}
],
"parameters": {}
}Call#
massIndex(input)Returns#
object with 9 fields: topic_id, title, state, ready, ready_at, series, latest, parameters, …
{
"topic_id": "D07-F02-A14",
"title": "Mass Index",
"state": "calculated",
"ready": true,
"ready_at": 40,
"series": {
"value": [null, null, null, null, null, null]
},
"latest": {
"value": 25.15692329607823
},
"parameters": {},
"diagnostics": {
"causal": true,
"input_count": 96
}
}Diagrams#
Calculation flow#
Mass Index calculation flow
flowchart LR
A["ordered OHLC or close observations with explicit window, s"] --> B["Validate order, basis, and finite values"]
B --> C["Apply the selected Mass Index convention"]
C --> D["Emit value, readiness, and diagnostics"]
D --> E["Interpret descriptively; test outcomes separately"]
B -->|invalid or insufficient| X["Withhold output with a reason"]
Mass Index readiness and evidence states
stateDiagram-v2
[*] --> Waiting
Waiting --> Ready: enough valid causal observations
Waiting --> Rejected: malformed or unsupported input
Ready --> Calculated: selected formula applied
Calculated --> Interpreted: diagnostic and limitation retained
Interpreted --> Ready: next observation arrives
Rejected --> Waiting: corrected input and deterministic reset
How it works#
This page states the contract — how to call it correctly. The article explains the concept: why it works, and where it breaks.
References#
- TA-Lib function groups — see linked primary or authoritative record
- TA-Lib C/C++ API — see linked primary or authoritative record
- TA-Lib maintained source — see linked primary or authoritative record
- Evidence decision
- Level 1 evidence map