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Transport, logistics and mobility
micromobility
scooter and bike fleet
Lime
System
Techniques · 22
Primitives · 89
micromobility
Deterministic simulation testing
distributed · medium: Run the whole system in one thread under a seeded scheduler with simulated network, disk and clock, so every failure replays from its seed.
›
Primary-backup replication
distributed · medium: One node orders all writes and ships them to standbys; the acknowledgement rule (none, one, all) sets what a crash loses, and an external arbiter decides who takes over.
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A/B partition updates
embedded · medium: Two bootable slots and a small atomic metadata block: write the new image to the idle slot, try it once, and fall back by itself unless it reports healthy.
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Payment state machine
finance · medium: Persisted state machine for a payment lifecycle (authorize, capture, void, refund) that treats timeouts as unknown, retries with the same key and applies webhooks idempotently.
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Min cost flow
graphs · medium: Minimum-cost flow (successive shortest paths, network simplex) for distribution and rebalancing
Large neighbourhood search (ruin an…
optimization · medium: Repeatedly remove a chunk of a solution and rebuild it with a heuristic or exact solver; learn which operator pairs pay off.
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Coverage-guided fuzzing
security · medium: Mutate inputs, run an instrumented target, and keep any input that reaches a new code edge; feedback turns blind guessing into incremental search.
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Idempotency keys
finance · low: Client-chosen unique key per logical operation, stored with a request fingerprint and the final response, so retries replay the first result instead of acting twice.
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Hierarchical state machine
systems · low: Nest states so a substate inherits its parent's reactions and only overrides what differs, with ordered entry and exit actions along the path.
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Kalman filter
robotics · low: Optimal recursive estimator for a linear system with Gaussian noise: fuses a motion model with noisy measurements into a state estimate plus its covariance.
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Hdr histogram
data-structures · low: Log-linear bucketed histograms with bounded relative error for latency percentiles
Low power duty cycling
embedded · low: MCU sleep states, wake sources and radio duty cycling to run years on a battery
Geodesic distance (haversine, Vince…
geometry · low: Shortest-path distance between two lat/lon points on the Earth: haversine on a sphere (about 0.5% error), Vincenty or Karney on the WGS84 ellipsoid (sub-millimetre).
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Geospatial cell index (geohash, S2,…
geometry · low: Map a lat/lon to a 64-bit cell id on a hierarchical grid, so "near" becomes an integer range scan in any ordinary sorted index.
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Point in polygon
geometry · low: Ray-casting/winding tests and indexed polygon lookup for reverse geocoding
R-tree
geometry · low: A balanced tree of nested bounding boxes that indexes rectangles and points, answering window and nearest-neighbour queries by pruning whole subtrees.
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Process supervision
hardware-os · low: A parent process starts services, reaps their exits and restarts them under a delay and burst-limit policy, then stops them with SIGTERM before SIGKILL.
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Mqtt protocol
networking · low: MQTT pub/sub: topics, QoS 0/1/2, retained messages, sessions and keepalive
Message authentication codes (HMAC,…
security · low: A keyed short tag proving a message is unmodified and came from a key holder; pick HMAC, CMAC, KMAC or a one-time polynomial MAC by what primitive you already have.
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Mutual TLS
security · low: TLS where the client also proves a certificate key, so every connection carries a verified, rotatable machine identity.
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Replay protection window
security · low: A highest-seen counter plus a bitmap of the last W numbers rejects duplicates and stale messages in O(1) with a few hundred bytes of state.
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Ble gatt
signal-processing · low: Bluetooth LE link layer, ATT/GATT services and characteristics, connection intervals and pairing
Graceful draining
systems · low: On a termination signal, stop taking new work, finish in-flight work until a deadline, tell clients to reconnect elsewhere, then exit; clients resume from a token.
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+ 15 more techniques
+ 73 more primitives
System
Techniques · 22
Primitives · 89
micromobility
Deterministic simulation testing
distributed · medium: Run the whole system in one thread under a seeded scheduler with simulated network, disk and clock, so every failure replays from its seed.
›
Primary-backup replication
distributed · medium: One node orders all writes and ships them to standbys; the acknowledgement rule (none, one, all) sets what a crash loses, and an external arbiter decides who takes over.
›
A/B partition updates
embedded · medium: Two bootable slots and a small atomic metadata block: write the new image to the idle slot, try it once, and fall back by itself unless it reports healthy.
›
Payment state machine
finance · medium: Persisted state machine for a payment lifecycle (authorize, capture, void, refund) that treats timeouts as unknown, retries with the same key and applies webhooks idempotently.
›
Min cost flow
graphs · medium: Minimum-cost flow (successive shortest paths, network simplex) for distribution and rebalancing
Large neighbourhood search (ruin an…
optimization · medium: Repeatedly remove a chunk of a solution and rebuild it with a heuristic or exact solver; learn which operator pairs pay off.
›
Coverage-guided fuzzing
security · medium: Mutate inputs, run an instrumented target, and keep any input that reaches a new code edge; feedback turns blind guessing into incremental search.
›
Time-series forecasting (baselines,…
statistics · medium: The end-to-end recipe: fix horizon and uncertainty, beat naive baselines, choose a model family, and validate with rolling-origin backtests and scale-free metrics.
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Point-in-time recovery
storage · medium: Periodic base backups plus a continuously archived change log let you rebuild the state as of any instant, then branch from there.
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Delta debugging
compilers · medium: Ddmin minimization of failing inputs or change sets
Binary delta diff
compression · medium: Bsdiff, VCDIFF and xdelta-style binary patches between file versions
Fault injection
distributed · medium: Inject latency, errors, kills and partitions via proxies, netem or hooks
Constraint propagation (constraint…
optimization · medium: Variables with finite domains, propagators that prune impossible values to a fixpoint, and backtracking search with trail undo between decisions.
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Simulated annealing
optimization · medium: Stochastic local search with a cooling schedule for combinatorial optimization
Signed update metadata (TUF)
security · medium: Separate signing roles with thresholds sign small metadata pinning file hashes, versions and expiry, so clients detect rollback, freeze and mix-and-match and recover by rotating the root.
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Arima
statistics · medium: ARIMA/SARIMA forecasting: differencing, AR and MA terms, order selection, maximum-likelihood fit
ARIES recovery
storage · medium: Three-pass crash recovery (analysis, redo, undo) for steal/no-force buffer pools; repeats history, then rolls back losers with compensation log records.
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Local search 2opt or opt
optimization · medium: 2-opt, Or-opt, relocate and swap neighborhoods with fast delta evaluation for routes
Key rotation
security · medium: Rotating keys without downtime: key ids, overlap windows, re-wrapping, JWKS publication, revocation
Syscall interception
security · medium: Intercept syscalls via ptrace, seccomp user notify or a user-space kernel
Buffer pool
storage · medium: The database's own page cache (frames, page table, pin counts, dirty bits, replacement) so it, not the OS, controls eviction, write order and I/O.
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Envelope encryption
security · medium: Encrypt each object with its own data key and wrap that key under a KMS-held key, so rotation re-wraps 60 bytes and deleting a key shreds data.
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Idempotency keys
finance · low: Client-chosen unique key per logical operation, stored with a request fingerprint and the final response, so retries replay the first result instead of acting twice.
›
Hierarchical state machine
systems · low: Nest states so a substate inherits its parent's reactions and only overrides what differs, with ordered entry and exit actions along the path.
›
Kalman filter
robotics · low: Optimal recursive estimator for a linear system with Gaussian noise: fuses a motion model with noisy measurements into a state estimate plus its covariance.
›
Hdr histogram
data-structures · low: Log-linear bucketed histograms with bounded relative error for latency percentiles
Low power duty cycling
embedded · low: MCU sleep states, wake sources and radio duty cycling to run years on a battery
Geodesic distance (haversine, Vince…
geometry · low: Shortest-path distance between two lat/lon points on the Earth: haversine on a sphere (about 0.5% error), Vincenty or Karney on the WGS84 ellipsoid (sub-millimetre).
›
Geospatial cell index (geohash, S2,…
geometry · low: Map a lat/lon to a 64-bit cell id on a hierarchical grid, so "near" becomes an integer range scan in any ordinary sorted index.
›
Point in polygon
geometry · low: Ray-casting/winding tests and indexed polygon lookup for reverse geocoding
R-tree
geometry · low: A balanced tree of nested bounding boxes that indexes rectangles and points, answering window and nearest-neighbour queries by pruning whole subtrees.
›
Process supervision
hardware-os · low: A parent process starts services, reaps their exits and restarts them under a delay and burst-limit policy, then stops them with SIGTERM before SIGKILL.
›
Mqtt protocol
networking · low: MQTT pub/sub: topics, QoS 0/1/2, retained messages, sessions and keepalive
Message authentication codes (HMAC,…
security · low: A keyed short tag proving a message is unmodified and came from a key holder; pick HMAC, CMAC, KMAC or a one-time polynomial MAC by what primitive you already have.
›
Mutual TLS
security · low: TLS where the client also proves a certificate key, so every connection carries a verified, rotatable machine identity.
›
Replay protection window
security · low: A highest-seen counter plus a bitmap of the last W numbers rejects duplicates and stale messages in O(1) with a few hundred bytes of state.
›
Ble gatt
signal-processing · low: Bluetooth LE link layer, ATT/GATT services and characteristics, connection intervals and pairing
Graceful draining
systems · low: On a termination signal, stop taking new work, finish in-flight work until a deadline, tell clients to reconnect elsewhere, then exit; clients resume from a token.
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Cooperative scheduling
concurrency · low: Green threads/coroutines yielding at await points on a user-space scheduler
Record replay
distributed · low: Record every nondeterministic input (time, randomness, I/O, model and tool outputs, per-tick player input) and re-execute deterministically for debugging, replays and state rebuild
PRNGs (PCG, xoshiro)
numerics · low: Small, fast, statistically strong non-cryptographic generators: PCG32 and xoshiro256**, with seeding, parallel streams and unbiased ranges.
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Leases
distributed · low: A lock that expires on its own: bounded-time ownership that survives crashes and partitions, given bounded clock drift and fencing tokens on writes.
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Write-ahead log
storage · low: Append each change to a checksummed sequential log and fsync it before touching data pages; the basis of crash durability in nearly every database.
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Health checking
systems · low: Decide per backend whether to route to it using probes and real-traffic errors, with consecutive-count hysteresis, capped ejection and a panic fallback.
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Watchdog timer
embedded · low: A hardware down-counter that resets the chip unless software proves, in time and in a plausible pattern, that it is still healthy.
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CRC32C checksums
hardware-os · low: The Castagnoli CRC-32 with dedicated instructions on x86 (SSE4.2) and ARMv8. It is the standard fast integrity check for storage blocks, logs and network frames.
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Secure boot chain
security · low: Each boot stage verifies the signature of the next before running it, anchored in an immutable ROM key hash, with version counters against downgrade and a TPM log of what ran.
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Event sourcing
finance · low: Persist state changes as an append-only stream of immutable events per entity; current state is a fold over them, guarded by expected-version appends.
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Exponential backoff with jitter
systems · low: Retry after delays that grow geometrically and are randomized, so failed clients spread out instead of hammering a recovering service in synchronized waves.
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d-ary heap
data-structures · low: Array heap with d children per node (d = 4 typical): half the binary heap's depth, siblings in one cache line, faster priority queues.
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Bellman ford negative cycles
graphs · low: Bellman-Ford shortest paths with negative edges and negative-cycle (arbitrage) detection
Dijkstra's algorithm
graphs · low: Single-source shortest paths with non-negative edge weights by settling vertices in order of distance with a priority queue.
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Code coverage instrumentation
compilers · low: Insert counters into compiled code to record which blocks, edges or lines ran; a spanning tree of the control-flow graph cuts the counters needed.
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Fast hash functions
data-structures · low: Non-cryptographic hashes built from 64×64→128-bit multiplies and xor-shifts; pick by key size, trust level and whether the hash is persisted.
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Sanitizers
security · low: ASan/UBSan/TSan shadow memory and instrumentation to catch memory bugs
Croston method
statistics · low: Forecasting intermittent demand by separately smoothing demand sizes and intervals (Croston, SBA, TSB)
Exponential smoothing (ETS, Holt-Wi…
statistics · low: Forecast by keeping a few running states (level, trend, seasonal) updated by a fraction of each forecast error; O(1) memory per series and a strong baseline.
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STL decomposition (seasonal-trend w…
statistics · low: Split a series into trend, seasonal and remainder with iterated loess smoothing; the seasonal shape may drift and robust weights keep outliers out of it.
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Time-series cross-validation (rolli…
statistics · low: Estimate forecast error by repeatedly training on the past and testing on the next h steps, moving the origin forward; never trains on the future.
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Object storage
cloud · low: S3-compatible blob storage at cents per GB-month with 11 nines durability; pick by egress price, request price and latency, not by storage price alone.
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Copy on write snapshots
storage · low: Point-in-time snapshots by sharing pages/extents and copying only on write
Failure bisection
search-sort · low: Binary search over commits, batches or inputs to isolate a failure
Delta encoding
compression · low: Store differences between consecutive values instead of the values, turning sorted IDs, timestamps and counters into small numbers that pack into few bits.
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LZ77
compression · low: Replace repeated byte strings with (distance, length) back-references into a sliding window; the parsing stage of gzip, LZ4, zstd, Brotli and xz.
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Rolling hash
data-structures · low: Rabin-Karp polynomial rolling hashes and winnowing for substring fingerprints and document matching
Suffix array
search-sort · low: Sorted array of all suffix start positions of a text; finds every occurrence of any substring by binary search, at 4-5 bytes per text byte.
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Transparent interception
networking · low: Redirect traffic to a local proxy (iptables TPROXY/REDIRECT, eBPF) without app changes
Interval arithmetic
numerics · low: Rigorous bounds with outward rounding; root isolation and robust geometric tests
Two watched literals
optimization · low: Unit propagation for SAT that watches just two literals per clause, so backtracking costs nothing and long clauses are rarely touched.
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Journaled state revert
storage · low: Undo journal of state writes enabling nested checkpoints and cheap revert
Deterministic serialization
finance · low: Canonical byte encodings (RLP, SSZ, canonical CBOR) so every node hashes identical bytes
Cryptographic hashes (SHA-2, BLAKE3)
security · low: Collision-resistant fingerprints of data; SHA-256 for interoperability, BLAKE3 for speed, HMAC/HKDF for keyed uses.
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Digital signatures (Ed25519)
security · low: Small, fast, deterministic public-key signatures that prove who produced a message; the default for tokens, releases and protocols.
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Finite differences
numerics · low: Replace derivatives with weighted differences of grid values; simple stencils plus a stability condition (CFL) turn PDEs like heat, advection and waves into array loops.
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L-BFGS
numerics · low: Quasi-Newton minimizer that approximates the inverse Hessian from the last m gradient differences via the two-loop recursion; O(m·n) memory and work per step.
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k-d tree
geometry · low: A binary tree that splits k-dimensional points by one coordinate per level, giving fast nearest-neighbour and box queries on static low-dimensional data.
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Secrets management
security · low: Keep keys and passwords out of code and logs, give workloads short-lived identity instead of static keys, and make rotation routine.
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Cron scheduling
systems · low: Cron expression parsing and next-fire-time computation, with catch-up and time-zone rules
Ebpf
hardware-os · low: Verified in-kernel programs on hooks (kprobes, XDP, tc) with maps
Ptrace process control
hardware-os · low: Ptrace: attach, read and write registers and memory, single-step, intercept signals
Seccomp bpf
security · low: Syscall filtering with seccomp BPF programs
fsync, O_DSYNC and O_DIRECT
hardware-os · low: What fsync, fdatasync, O_DSYNC, O_DIRECT and F_FULLFSYNC really guarantee on Linux and macOS, and the exact call sequences for crash-safe files.
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LRU and CLOCK
systems · low: LRU evicts the least recently used entry via hash map plus linked list; CLOCK approximates it with a reference bit, so hits take no lock.
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S3-FIFO
systems · low: Three FIFO queues (small, main, ghost) that evict one-hit wonders quickly and keep reused objects; low miss ratios with no list moves on hits.
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AEAD (AES-GCM, ChaCha20-Poly1305)
security · low: Authenticated encryption that encrypts and detects tampering in one call; the only kind of symmetric encryption you should use.
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Aes key wrap
security · low: AES Key Wrap (RFC 3394/5649) and AES-GCM-SIV for deterministic, authenticated wrapping of key material
Csprng
security · low: OS-backed cryptographically secure random numbers (getrandom), and when a fast PRNG is not enough
Control-flow graph
compilers · low: Split a linear instruction list into basic blocks and connect them by jumps; the graph every optimizer, SSA builder and dataflow pass walks.
›
Bit packing and PFOR
compression · low: Store blocks of integers with exactly b bits each and patch rare outliers separately (PFOR); the fastest integer codec family, billions of values per second.
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Varint (LEB128)
compression · low: Variable-length integers in 7-bit groups with a continuation bit; small numbers take 1 byte, the wire format of Protobuf, WebAssembly and DWARF.
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Fencing tokens
distributed · low: A number that grows with every lock grant and is checked by the protected resource, so a paused ex-holder's late write is rejected.
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Quadtree octree
geometry · low: Adaptive spatial subdivision trees for queries and level of detail; loose and linear variants
Space filling curves
geometry · low: Z-order/Morton (geohash) and Hilbert curves mapping multi-dimensional points to sortable keys
BFS and DFS
graphs · low: The two basic graph traversals; BFS gives hop distances and levels, DFS gives discovery/finish order for cycles, components and topological order.
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Minimum spanning tree
graphs · low: Cheapest set of edges connecting all vertices; Kruskal sorts edges and joins components with union-find, Prim grows one tree, Boruvka merges in parallel rounds.
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Union-find
graphs · low: Disjoint-set forest with union by size and path compression; merges sets and answers same-set queries in effectively constant time.
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SIMD programming
hardware-os · low: Process 4-16 lanes per instruction with AVX2, AVX-512 or NEON via Rust std::arch, with runtime dispatch and a portable fallback.
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Evaluation metrics
machine-learning · low: Precision, recall, ROC AUC, average precision, log loss, NDCG and pass@k computed correctly, plus paired confidence intervals for comparing models.
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Loss functions
machine-learning · low: The scalar a model minimizes: cross-entropy for classes and tokens, MSE or Huber for values, each with a stable form and simple gradient.
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Explicit Euler
numerics · low: Step an ODE forward by its current slope, y += h·f(t, y); first-order, one evaluation per step, the baseline every other integrator is measured against.
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LU and Cholesky factorization
numerics · low: Factor A = PLU (any square matrix, partial pivoting) or A = LLᵀ (SPD) once in O(n³), then solve each right-hand side in O(n²).
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Newton root finding
numerics · low: Linearize at the guess and jump to the tangent root; quadratic convergence near a simple root, made robust by brackets (1D) or line search.
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Sparse matrices (CSR)
numerics · low: Compressed sparse row stores only nonzeros as row pointers, column indices and values; SpMV streams them once, so it is memory-bandwidth bound.
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Thomas tridiagonal solver
numerics · low: O(n) tridiagonal linear solve used in implicit finite-difference and spline schemes
Radix sort
search-sort · low: Non-comparison sort that distributes keys by 8-bit digits; several times faster than comparison sorts on large arrays of integers, floats or fixed-size keys.
›
Constant time code
security · low: Writing secret-dependent code without branches or memory lookups on secrets; constant-time compare and select
JSON Web Token (JWT)
security · low: A signed, URL-safe token carrying claims; the verifier's job is the checklist (pinned algorithm, key by kid, exp, aud, iss), not the format.
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OAuth 2 and OpenID Connect
security · low: Delegated authorization (OAuth 2) and login on top of it (OIDC); use authorization code + PKCE for every user-facing client.
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Bootstrap confidence intervals
statistics · low: Resampling-based confidence intervals for arbitrary statistics
Robust statistics
statistics · low: Location and scale estimates (median, MAD, trimmed mean, Huber M-estimator) that stay correct when a minority of the data is garbage.
›
Optimistic concurrency control
storage · low: Run transactions without locks, record what they read, and validate at commit that nothing changed; fastest when conflicts are rare.
›
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