SOFTWARE ENGINEERING COMPANY

We write the algorithm,
then run it in production.

PGIM builds software for businesses. Every system on this site is running in production — and comes with its algorithm, summarised from the source that runs it.

See the systems Services

CandidateSearchOperator.cs — hybrid retrieval + RRF

BM25Index:  k1 = 1.5,  b = 0.75
  idf   = log((N − df + 0.5) / (df + 0.5) + 1)
  norm  = k1 · (1 − b + b · |d| / avgdl)
  score = idf · tf·(k1 + 1) / (tf + norm)

pipeline(jd, filters):
  1  dimIds  ← sql_filter(filters)              # lọc trước theo chiều cấu trúc
  2  ‖ bm25  ← bm25(jd, top = 200) ∩ dimIds     # chạy song song
     ‖ embed ← ann(embed(jd), top = 200)
  3  rrf[d]  ← Σ_lists 1 / (k + rank_i + 1),  k = 60
     pool    ← top 30 by rrf                    # hợp nhất, không cần chuẩn hoá thang điểm
  4  for c in pool (semaphore-bounded):
       eval[c] ← ‖ llm_judge(c, jd, view = CTO)
                 ‖ llm_judge(c, jd, view = HR)
  5  boost   ← apply_feedback(eval)
  6  return top 10 by overall_score

From CandidateSearchOperator.cs — the candidate ranking system running at chat.rentaicoder.com. Every number is the number in the code.

§ 01 — CORE TECHNIQUES

Six techniques, reused across the systems

We do not reinvent the approach every project. These are the techniques we have pushed to production, and where each one runs.

Rank fusion with RRF

Two retrieval paths produce two score scales that cannot be compared. Reciprocal Rank Fusion discards the scores and uses rank alone — so there is no weight to choose, and every weight would have been a guess.

score(d) = Σ 1 / (k + rank_i(d)),  k = 60

ATS — Multi-agent candidate ranking

Five-layer fractal architecture

Every module at every depth has the same shape. The dependency rules become derivable from the path instead of memorised — new engineers and AI agents both find their way.

module ::= { Bootstrap, Operators, Core, Impl, Boundary }

Abstract Driven Development V3 VDG POS Counter EDU ChatBot Xăng Gate VDG FreightForwarder

Domains modelled as state machines

Valid states and valid transitions are declared explicitly. An invalid transition is blocked by an error carrying context, rather than silently corrected while the data quietly rots.

(s, e) ∉ δ  ⇒  Err(InvalidTransition { from: s, event: e })

VDG FreightForwarder

Trust modelled by data region

Within one string, the part the system generated and the part a user typed carry different trust. Sensitive values are only read from the region the other side does not control.

amount ← parse(text[0 .. index_of(note_marker)])

BankBridge

Multi-tier degradation ladders

Provider quotas are metered along several independent axes. Turning each axis into its own fallback tier makes them stack, and a long-running task no longer dies halfway.

profile → project → model

Xăng Gate

Push the compute to the client

Sensitive data should not leave the operator's machine. Compiling the business core to WebAssembly leaves a deliverable of plain static files — with no server there to leak from.

parse ∘ validate ∘ transition  ⊂  WebAssembly

VDG FreightForwarder

§ 02 — SYSTEM INDEX

Every system, with its core algorithm

Follow a name to read the full algorithm section, with pseudocode and the reasoning behind the choice.

#	System	Core algorithm	Built with
01	ATS — Multi-agent candidate rankingchat.rentaicoder.com	CandidateSearchOperator.cs — hybrid retrieval + RRF	.NET 10 · NTG.Adk · EmbeddingGemma · SQLite · SSE
02	Vietnamese Legal AI Assistantchat.rentaicoder.com/law.html	LawChatOperator.cs — agent tự chọn công cụ tra cứu	.NET 10 · NTG.Adk · BM25 · ONNX · SQLite
03	Abstract Driven Development V3abstractdriven.com · MIT	F.A.P — fractal architecture pattern	Open source · MIT · llms.txt
04	BankBridgemonorepo: ESP32 · Node · Android	server/parser.js — mô hình tin cậy 3 lớp	ESP32-S3 · PlatformIO · Node.js · Socket.IO · SQLite · Kotlin
05	VDG FreightForwarderstatic build: HTML + JS + .wasm	src/abstractions/states — 28 máy trạng thái thuần Rust	Rust · wasm-bindgen · calamine · Lit · AG Grid
06	EDU ChatBotedu.rentaicoder.com	HandoverOperator.cs — luật leo thang sang người thật	.NET 10 · EF Core · A.D.D V3 · LLM tool-calling
07	VDG POS Counterpos.rentaicoder.com · desktop + web	Ràng buộc pháp lý — ở đây quy định chính là đặc tả	.NET 10 · Avalonia 11 · EF Core 10 · SQLite WAL · Quartz.NET · ESC/POS
08	VDG FundTrailRust core · Android + web	Quét approval TRC20 — rủi ro nằm ở quyền đã cấp, không ở số dư	Rust · TRON / TRC20 · Android · Web
09	Xăng Gatexanggate.rentaicoder.com	Tách dịch vụ, xác thực bằng khoá bất đối xứng	Lit 3 · Vite · ASP.NET Core 10 · Docker · JWT RS256
10	Vang An Thinhvanganthinh.com	Bảng giá: poll 30s → Strapi proxy → vang.today	Astro · Alpine.js · Tailwind CSS · Strapi · Docker
11	ACP — Asia Consumer Productsacp.net.vn	render-static.js — dựng sẵn lúc build, không render lúc chạy	EJS · Static render · Netlify
12	Cashback Tradecashbacktrade.pro	Quy kết giới thiệu — mô tả từ luồng công khai, KHÔNG đọc được mã nguồn	—
13	JinkyTRXtrone.cashbacktrade.pro	Đăng nhập không mật khẩu qua bot Telegram — quan sát từ màn xác thực	—

§ 03 — SELECTED

Six systems worth reading first

Each one carries its own algorithm section. Products without screenshots show their pseudocode instead.

ATS — Multi-agent candidate ranking

chat.rentaicoder.com

A recruitment system that ranks candidates through two independent retrieval paths, merges them with Reciprocal Rank Fusion, then has an LLM score the survivors from two perspectives.

Read the detail