Migrate docs from Sphinx to MkDocs (#18145)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/models/generative_models.md

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+---
+title: Generative Models
+---
+[](){ #generative-models }
+
+vLLM provides first-class support for generative models, which covers most of LLMs.
+
+In vLLM, generative models implement the [VllmModelForTextGeneration][vllm.model_executor.models.VllmModelForTextGeneration] interface.
+Based on the final hidden states of the input, these models output log probabilities of the tokens to generate,
+which are then passed through [Sampler][vllm.model_executor.layers.Sampler] to obtain the final text.
+
+For generative models, the only supported `--task` option is `"generate"`.
+Usually, this is automatically inferred so you don't have to specify it.
+
+## Offline Inference
+
+The [LLM][vllm.LLM] class provides various methods for offline inference.
+See [configuration][configuration] for a list of options when initializing the model.
+
+### `LLM.generate`
+
+The [generate][vllm.LLM.generate] method is available to all generative models in vLLM.
+It is similar to [its counterpart in HF Transformers](https://huggingface.co/docs/transformers/main/en/main_classes/text_generation#transformers.GenerationMixin.generate),
+except that tokenization and detokenization are also performed automatically.
+
+```python
+from vllm import LLM
+
+llm = LLM(model="facebook/opt-125m")
+outputs = llm.generate("Hello, my name is")
+
+for output in outputs:
+    prompt = output.prompt
+    generated_text = output.outputs[0].text
+    print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
+```
+
+You can optionally control the language generation by passing [SamplingParams][vllm.SamplingParams].
+For example, you can use greedy sampling by setting `temperature=0`:
+
+```python
+from vllm import LLM, SamplingParams
+
+llm = LLM(model="facebook/opt-125m")
+params = SamplingParams(temperature=0)
+outputs = llm.generate("Hello, my name is", params)
+
+for output in outputs:
+    prompt = output.prompt
+    generated_text = output.outputs[0].text
+    print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
+```
+
+!!! warning
+    By default, vLLM will use sampling parameters recommended by model creator by applying the `generation_config.json` from the huggingface model repository if it exists. In most cases, this will provide you with the best results by default if [SamplingParams][vllm.SamplingParams] is not specified.
+
+    However, if vLLM's default sampling parameters are preferred, please pass `generation_config="vllm"` when creating the [LLM][vllm.LLM] instance.
+A code example can be found here: <gh-file:examples/offline_inference/basic/basic.py>
+
+### `LLM.beam_search`
+
+The [beam_search][vllm.LLM.beam_search] method implements [beam search](https://huggingface.co/docs/transformers/en/generation_strategies#beam-search) on top of [generate][vllm.LLM.generate].
+For example, to search using 5 beams and output at most 50 tokens:
+
+```python
+from vllm import LLM
+from vllm.sampling_params import BeamSearchParams
+
+llm = LLM(model="facebook/opt-125m")
+params = BeamSearchParams(beam_width=5, max_tokens=50)
+outputs = llm.beam_search([{"prompt": "Hello, my name is "}], params)
+
+for output in outputs:
+    generated_text = output.sequences[0].text
+    print(f"Generated text: {generated_text!r}")
+```
+
+### `LLM.chat`
+
+The [chat][vllm.LLM.chat] method implements chat functionality on top of [generate][vllm.LLM.generate].
+In particular, it accepts input similar to [OpenAI Chat Completions API](https://platform.openai.com/docs/api-reference/chat)
+and automatically applies the model's [chat template](https://huggingface.co/docs/transformers/en/chat_templating) to format the prompt.
+
+!!! warning
+    In general, only instruction-tuned models have a chat template.
+    Base models may perform poorly as they are not trained to respond to the chat conversation.
+
+```python
+from vllm import LLM
+
+llm = LLM(model="meta-llama/Meta-Llama-3-8B-Instruct")
+conversation = [
+    {
+        "role": "system",
+        "content": "You are a helpful assistant"
+    },
+    {
+        "role": "user",
+        "content": "Hello"
+    },
+    {
+        "role": "assistant",
+        "content": "Hello! How can I assist you today?"
+    },
+    {
+        "role": "user",
+        "content": "Write an essay about the importance of higher education.",
+    },
+]
+outputs = llm.chat(conversation)
+
+for output in outputs:
+    prompt = output.prompt
+    generated_text = output.outputs[0].text
+    print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
+```
+
+A code example can be found here: <gh-file:examples/offline_inference/basic/chat.py>
+
+If the model doesn't have a chat template or you want to specify another one,
+you can explicitly pass a chat template:
+
+```python
+from vllm.entrypoints.chat_utils import load_chat_template
+
+# You can find a list of existing chat templates under `examples/`
+custom_template = load_chat_template(chat_template="<path_to_template>")
+print("Loaded chat template:", custom_template)
+
+outputs = llm.chat(conversation, chat_template=custom_template)
+```
+
+## Online Serving
+
+Our [OpenAI-Compatible Server][openai-compatible-server] provides endpoints that correspond to the offline APIs:
+
+- [Completions API][completions-api] is similar to `LLM.generate` but only accepts text.
+- [Chat API][chat-api]  is similar to `LLM.chat`, accepting both text and [multi-modal inputs][multimodal-inputs] for models with a chat template.