[Doc] Move examples into categories (#11840)

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

examples/offline_inference/offline_inference_encoder_decoder.py

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+'''
+Demonstrate prompting of text-to-text
+encoder/decoder models, specifically BART
+'''
+
+from vllm import LLM, SamplingParams
+from vllm.inputs import (ExplicitEncoderDecoderPrompt, TextPrompt,
+                         TokensPrompt, zip_enc_dec_prompts)
+
+dtype = "float"
+
+# Create a BART encoder/decoder model instance
+llm = LLM(
+    model="facebook/bart-large-cnn",
+    dtype=dtype,
+)
+
+# Get BART tokenizer
+tokenizer = llm.llm_engine.get_tokenizer_group()
+
+# Test prompts
+#
+# This section shows all of the valid ways to prompt an
+# encoder/decoder model.
+#
+# - Helpers for building prompts
+text_prompt_raw = "Hello, my name is"
+text_prompt = TextPrompt(prompt="The president of the United States is")
+tokens_prompt = TokensPrompt(prompt_token_ids=tokenizer.encode(
+    prompt="The capital of France is"))
+# - Pass a single prompt to encoder/decoder model
+#   (implicitly encoder input prompt);
+#   decoder input prompt is assumed to be None
+
+single_text_prompt_raw = text_prompt_raw  # Pass a string directly
+single_text_prompt = text_prompt  # Pass a TextPrompt
+single_tokens_prompt = tokens_prompt  # Pass a TokensPrompt
+
+# - Pass explicit encoder and decoder input prompts within one data structure.
+#   Encoder and decoder prompts can both independently be text or tokens, with
+#   no requirement that they be the same prompt type. Some example prompt-type
+#   combinations are shown below, note that these are not exhaustive.
+
+enc_dec_prompt1 = ExplicitEncoderDecoderPrompt(
+    # Pass encoder prompt string directly, &
+    # pass decoder prompt tokens
+    encoder_prompt=single_text_prompt_raw,
+    decoder_prompt=single_tokens_prompt,
+)
+enc_dec_prompt2 = ExplicitEncoderDecoderPrompt(
+    # Pass TextPrompt to encoder, and
+    # pass decoder prompt string directly
+    encoder_prompt=single_text_prompt,
+    decoder_prompt=single_text_prompt_raw,
+)
+enc_dec_prompt3 = ExplicitEncoderDecoderPrompt(
+    # Pass encoder prompt tokens directly, and
+    # pass TextPrompt to decoder
+    encoder_prompt=single_tokens_prompt,
+    decoder_prompt=single_text_prompt,
+)
+
+# - Finally, here's a useful helper function for zipping encoder and
+#   decoder prompts together into a list of ExplicitEncoderDecoderPrompt
+#   instances
+zipped_prompt_list = zip_enc_dec_prompts(
+    ['An encoder prompt', 'Another encoder prompt'],
+    ['A decoder prompt', 'Another decoder prompt'])
+
+# - Let's put all of the above example prompts together into one list
+#   which we will pass to the encoder/decoder LLM.
+prompts = [
+    single_text_prompt_raw, single_text_prompt, single_tokens_prompt,
+    enc_dec_prompt1, enc_dec_prompt2, enc_dec_prompt3
+] + zipped_prompt_list
+
+print(prompts)
+
+# Create a sampling params object.
+sampling_params = SamplingParams(
+    temperature=0,
+    top_p=1.0,
+    min_tokens=0,
+    max_tokens=20,
+)
+
+# Generate output tokens from the prompts. The output is a list of
+# RequestOutput objects that contain the prompt, generated
+# text, and other information.
+outputs = llm.generate(prompts, sampling_params)
+
+# Print the outputs.
+for output in outputs:
+    prompt = output.prompt
+    encoder_prompt = output.encoder_prompt
+    generated_text = output.outputs[0].text
+    print(f"Encoder prompt: {encoder_prompt!r}, "
+          f"Decoder prompt: {prompt!r}, "
+          f"Generated text: {generated_text!r}")