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Sampling and penalty techniques in mistral.rs

mistral.rs supports a comprehensive set of sampling and penalty techniques to control text generation. These can be configured via the HTTP API, Python SDK, or Rust SDK.

Temperature

Controls the randomness of token selection. Lower values make output more deterministic, higher values increase creativity and randomness.

  • Range: 0.0 to 2.0 (typically 0.0 to 1.0)
  • Default: Model-dependent, usually around 0.7
  • Effect: At 0.0, always selects the most likely token (greedy). At higher values, sampling becomes more diverse.

Top K

Limits token selection to the K most likely tokens.

  • Range: 1 to vocabulary size
  • Effect: Lower values restrict choices to only the most probable tokens, reducing randomness.

Top P (Nucleus Sampling)

Limits token selection to the smallest set of tokens whose cumulative probability exceeds P.

  • Range: 0.0 to 1.0
  • Effect: At 0.1, only tokens comprising the top 10% probability mass are considered. More adaptive than Top K as it adjusts based on the probability distribution.

Min P

Filters out tokens with probability less than min_p * max_probability.

  • Range: 0.0 to 1.0
  • Effect: Removes low-probability tokens relative to the most likely token. Useful for preventing unlikely tokens from being selected.

Stop Sequences

Strings that, when generated, cause generation to stop immediately.

  • Type: Array of strings
  • Effect: Generation terminates as soon as any stop sequence is produced. Useful for controlling output boundaries.

Repetition Penalty

Applies a multiplicative penalty to tokens that have already appeared in the context.

  • Range: Typically 1.0 to 2.0
  • Effect: Values > 1.0 make repeated tokens less likely. This is distinct from frequency and presence penalties.

Frequency Penalty

Penalizes tokens based on how many times they've appeared in the generated text so far.

  • Range: -2.0 to 2.0
  • Effect: Positive values reduce repetition proportionally to token frequency. Negative values encourage repetition.

Presence Penalty

Penalizes tokens that have appeared at least once in the generated text.

  • Range: -2.0 to 2.0
  • Effect: Positive values discourage any repetition (binary penalty). Negative values encourage reusing tokens.

DRY (Don't Repeat Yourself) Penalty

An advanced anti-repetition technique that detects and penalizes repeated sequences of tokens, not just individual tokens. See the original implementation for details.

DRY Parameters

  • dry_multiplier: Controls the strength of the penalty. Higher values more strongly discourage repetition.
  • dry_base: Base value for the exponential penalty calculation.
  • dry_allowed_length: Minimum sequence length before the penalty applies. Sequences shorter than this are not penalized.
  • dry_sequence_breakers: Array of tokens (like newlines, punctuation) that reset the sequence tracking. When these tokens appear, the DRY penalty starts fresh.

Example DRY Configuration (HTTP API)

{
  "dry_multiplier": 0.8,
  "dry_base": 1.75,
  "dry_allowed_length": 2,
  "dry_sequence_breakers": ["\n", ".", "!", "?", ";"]
}

API Usage

All sampling parameters can be set in API requests:

HTTP API

{
  "model": "default",
  "messages": [...],
  "temperature": 0.7,
  "top_p": 0.9,
  "top_k": 40,
  "min_p": 0.05,
  "repetition_penalty": 1.1,
  "frequency_penalty": 0.5,
  "presence_penalty": 0.5,
  "stop": ["END", "\n\n"],
  "dry_multiplier": 0.8,
  "dry_base": 1.75,
  "dry_allowed_length": 2,
  "dry_sequence_breakers": ["\n"]
}

Python SDK

response = runner.send_chat_completion_request(
    ChatCompletionRequest(
        model="default",
        messages=[...],
        temperature=0.7,
        top_p=0.9,
        top_k=40,
        min_p=0.05,
        repetition_penalty=1.1,
        frequency_penalty=0.5,
        presence_penalty=0.5,
        stop_seqs=["END", "\n\n"],
        dry_multiplier=0.8,
        dry_base=1.75,
        dry_allowed_length=2,
        dry_sequence_breakers=["\n"],
    )
)

Please suggest more sampling techniques by raising an issue!