Representation and Parameter Analysis

Extract concept directions from model features and weights to analyze and steer LLM behavior.

75|7|Updated May 2, 2026
One-click install
npx skills add https://github.com/zjunlp/Mechanist --skill representation-and-parameter-analysis-zjunlp
Or copy as Structured Prompt for Agent
Please help me install this Agent Skill.
Skill: Representation and Parameter Analysis
Source: https://github.com/zjunlp/Mechanist/tree/main/skills/mechanism-skills/representation-and-parameter-analysis
Command: npx skills add https://github.com/zjunlp/Mechanist --skill representation-and-parameter-analysis-zjunlp

SYSTEM DOCUMENTATION & REQUIREMENTS

💡 This Skill requires torch, transformers, sae-lens, accelerate, numpy, einops, datasets, matplotlib, seaborn, scikit-learn, python-dotenv, pandas, scipy, and includes scripts (resource) and references (resource) components.

What problem does it solve? Interpreting and controlling large language models usually requires expensive fine-tuning or exhaustive intervention sweeps. This Skill provides a unified workflow for reading and editing a model's internal objects — hidden-state features and weight parameters — using linear-algebra techniques, so interpretability findings translate directly into behavioral control without retraining. ## Core Features & Use Cases - Representation Engineering: Extract concept directions from contrastive prompt pairs to detect truthfulness, emotion, or harmlessness, and inject them back to steer generation. - Steering Vectors and Feature Steering: Build Contrastive Activation Addition vectors or directly amplify a selected feature (optionally via a Sparse Autoencoder) to control chat model behavior at inference time. - Parameter-Space Task Vectors: Compute weight differences between fine-tuned and pre-trained checkpoints, then add, negate, or combine them for multi-task composition or unlearning. - Use Case: A researcher wants to reduce sycophancy in Llama 2. They generate a steering vector from contrastive examples, apply it at a chosen layer during generation, and evaluate behavioral change across multiplier values. ## Quick Start Ask the assistant to steer the target model away from an undesired behavior using feature steering, checking first whether a Sparse Autoencoder exists for that model.

Frequently Asked Questions about Representation and Parameter Analysis

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I steer a language model's behavior without fine-tuning?

Extract a concept direction from contrastive prompt pairs using PCA or mean-difference on hidden-state activations, then add it back into the residual stream during generation. Steering vectors (CAA) and SAE feature clamping are the two main implementations covered.

What is the difference between steering vectors and SAE feature steering?

Steering vectors add a dense contrastive direction to the residual stream, while feature steering amplifies one isolated, near-monosemantic feature — optionally inside a Sparse Autoencoder via encode, amplify, decode. Feature steering is more targeted and less entangled, and is the recommended default.

Do I need a Sparse Autoencoder for feature steering?

No. An SAE is optional — the same direct-intervention method applies to a feature identified in the model's own backbone activations, scaled in place without any encode/decode step. If a released SAE exists for your model and layer, prefer it for cleaner, more monosemantic features.

How do task vectors edit models with arithmetic?

A task vector is the weight difference between a fine-tuned and pre-trained checkpoint. Adding vectors composes multi-task capabilities, negating one unlearns a behavior, and analogy-style combinations transfer skills — all applied to CLIP checkpoints without further training.

What are the limitations of linear representation steering?

The approach assumes concepts are linearly encoded; non-linear or entangled representations cause missed signal and off-target edits. Directions rarely transfer across models or checkpoints, and large steering coefficients push the model off-distribution, degrading fluency.