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LLM Basic Notes

Generative AI​

Generative Model​

  • Autoregressive (AR) model: generate output one token at a time, conditioned on previous tokens.
  • Non-autoregressive (NAR) model: generate output all at once parallel, without conditioning on previous tokens.
AR ModelNAR Model
ParallelismLowHigh
SpeedSlowFast
QualityHighLow

结合上述两种方法 (Encoder + Decoder 架构):

  • 用 AR model 生成中间向量, 用 NAR model 生成最终输出.
  • 用 NAR model 多次生成, 逐步优化输出.
  • Speculative decoding: 用 NAR model 快速生成若干个预测输出, 作为 AR model 的后续输入, 使得 AR model 可以同时输出多个结果.

Generative Model

Scaling Law​

现有的预训练语言模型对于数据的需求量远高于扩展法则 (e.g Chinchilla) 中所给出的估计规模. 很多更小的模型也能够通过使用超大规模的预训练数据获得较大的模型性能提升. 这种现象的一个重要原因是由于 Transformer 架构具有较好的数据扩展性. 目前为止, 还没有实验能够有效验证特定参数规模语言模型的饱和数据规模 (即随着数据规模的扩展, 模型性能不再提升).

Emergent Ability​

大语言模型的涌现能力被非形式化定义为 在小型模型中不存在但在大模型中出现的能力:

  • In-context learning.
  • Instruction following.
  • Step-by-step reasoning.

ChatGPT​

Fine-tuned GPT model on conversational data:

  • Pre-training: 学习文字接龙, 学习大规模资料 (self-supervised learning), 生成下一个单词.
  • Instruction-tuning (IT): 人工文字接龙, 人工标注部分问题的答案 (supervised learning), 引导模型生成的方向.
  • Reinforcement learning from human feedback (RLHF): 训练一个 reward model, 负责评价模型生成的答案, 提供人类反馈. 以 reward model 的评价分数为 reward, 通过强化学习优化模型. 一般聚焦于三个方面: 有用性 (Helpfulness), 诚实性 (Honesty), 无害性 (Harmlessness).
Alignment

Instruction-tuning (IT) with supervised learning on labelled data and reinforcement learning from human feedback (RLHF).

Diffusion Model​

Forward process (diffusion) + reverse process (denoise):

Diffusion Model

Stable diffusion model:

Stable Diffusion

Video Model​

Generative videos as world models simulator.

LLM Toolchain​

LangChain​

LangChain aims to make programming with LLMs easier.

LangChain Modules

Model I/O module normalize LLM inputs (e.g. prompts), APIs, and outputs (e.g. completions):

LangChain Model I/O Module

import { CommaSeparatedListOutputParser } from '@langchain/core/output_parsers'
import { PromptTemplate } from '@langchain/core/prompts'
import { OpenAI } from '@langchain/openai'

const template = PromptTemplate.fromTemplate('List 10 {subject}.\n{format_instructions}')
const model = new OpenAI({ temperature: 0 })
const listParser = new CommaSeparatedListOutputParser()

const prompt = await template.format({
  subject: 'countries',
  format_instructions: listParser.getFormatInstructions(),
})

const result = await model.invoke(prompt)

const listResult = await parser.parse(result)

Retrieval module help to process data alongside the user inputs, making it easier to retrieve relevant information:

LangChain Retrieval Module

import { UpstashVectorStore } from '@langchain/community/vectorstores/upstash'
import { OpenAIEmbeddings } from '@langchain/openai'
import { CSVLoader } from 'langchain/document_loaders/fs/csv'
import { ScoreThresholdRetriever } from 'langchain/retrievers/score_threshold'
import { RecursiveCharacterTextSplitter } from 'langchain/text_splitter'

// CSV data.
const loader = new CSVLoader('path/to/example.csv')
const docs = await loader.load()

// Text splitter.
const splitter = new RecursiveCharacterTextSplitter({
  chunkSize: 10,
  chunkOverlap: 1,
})
const docs = await splitter.createDocuments(['...'])

// Embeddings and vector store.
const vectorStore = new UpstashVectorStore(new OpenAIEmbeddings())
await vectorStore.addDocuments(docs)
const retriever = ScoreThresholdRetriever.fromVectorStore(vectorStore, {
  minSimilarityScore: 0.9,
})
const result = await retriever.getRelevantDocuments('...?')

Chains module link tasks together:

LangChain Chains Module

import { CommaSeparatedListOutputParser } from '@langchain/core/output_parsers'
import { PromptTemplate } from '@langchain/core/prompts'
import { RunnableSequence } from '@langchain/core/runnables'
import { OpenAI } from '@langchain/openai'

const template = PromptTemplate.fromTemplate('List 10 {subject}.\n{format_instructions}')
const model = new OpenAI({ temperature: 0 })
const listParser = new CommaSeparatedListOutputParser()

const chain = RunnableSequence.from([template, model, listParser])

const result = await chain.invoke({
  subject: 'countries',
  format_instructions: listParser.getFormatInstructions(),
})

Agents module is chains with a list of functions (called tools) it can execute, while chains are hardcoded, agents choose their actions with the help of an LLM:

LangChain Agents Module

import { createVectorStoreAgent, VectorStoreToolkit } from 'langchain/agents'

const toolkit = new VectorStoreToolkit({ name: 'Demo Data', vectorStore }, model)
const agent = createVectorStoreAgent(model, toolkit)

const result = await agent.invoke({ input: '...' })

LLM Platform​

  • OpenAI GPT API.
  • Google Gemini API.

AI Agents​

AI agents powered by tricky LLMs prompting:

MCP Server​

LLM Reference​