Add Ministral/Mistral model implementation (#5)

Implements Ministral-style models with:
- YaRN RoPE (Yet another RoPE extension) for extended context
- GQA (Grouped Query Attention) with configurable num_key_value_heads
- SwiGLU MLP with SiLU activation
- RMSNorm

Verified against HuggingFace transformers MistralForCausalLM with
max diff ~6e-7 (floating point precision).

Includes tests for:
- Loading pretrained Mistral-7B and comparing logits
- Creating models with custom config
- Text generation with streaming output

Co-authored-by: Claude <noreply@anthropic.com>

Author: dfalbel

R/ministral.R

@@ -0,0 +1,331 @@
+# References:
+# - https://huggingface.co/mistralai/Ministral-3-14B-Instruct-2512
+# - https://github.com/huggingface/transformers/blob/main/src/transformers/models/mistral/modeling_mistral.py
+
+#' @noRd
+#' @importFrom zeallot %<-%
+#' @importFrom purrr map
+#' @import torch
+NULL
+
+# YaRN RoPE helper functions
+yarn_find_correction_dim <- function(num_rotations, dim, base, max_position_embeddings) {
+  (dim * log(max_position_embeddings / (num_rotations * 2 * pi))) / (2 * log(base))
+}
+
+yarn_find_correction_range <- function(low_rot, high_rot, dim, base, max_position_embeddings) {
+  low <- floor(yarn_find_correction_dim(low_rot, dim, base, max_position_embeddings))
+  high <- ceiling(yarn_find_correction_dim(high_rot, dim, base, max_position_embeddings))
+  c(max(low, 0), min(high, dim - 1))
+}
+
+yarn_linear_ramp_mask <- function(min_val, max_val, dim, dtype = torch_float32()) {
+  if (min_val == max_val) min_val <- min_val - 0.001
+  linear_func <- (torch_arange(0, dim - 1, dtype = dtype) - min_val) / (max_val - min_val)
+  torch_clamp(linear_func, 0, 1)
+}
+
+ministral_rotate_half <- function(x) {
+  c(x1, x2) %<-% torch_split(x, x$size(-1) / 2, -1)
+  torch_cat(list(-x2, x1), dim = -1)
+}
+
+repeat_kv <- function(hidden_states, n_rep) {
+  if (n_rep == 1) return(hidden_states)
+  c(batch, num_kv_heads, seq_len, head_dim) %<-% hidden_states$shape
+  hidden_states$unsqueeze(3)$
+    expand(c(batch, num_kv_heads, n_rep, seq_len, head_dim))$
+    reshape(c(batch, num_kv_heads * n_rep, seq_len, head_dim))
+}
+
+nn_ministral_rmsnorm <- nn_module(
+  initialize = function(hidden_size, eps = 1e-5) {
+    self$weight <- nn_parameter(torch_ones(hidden_size))
+    self$eps <- eps
+  },
+  forward = function(x) {
+    dtype <- x$dtype
+    variance <- x$to(dtype = "float32")$pow(2)$mean(-1, keepdim = TRUE)
+    x <- x * torch_rsqrt(variance + self$eps)
+    (self$weight * x)$to(dtype = dtype)
+  }
+)
+
+nn_ministral_yarn_rotary_embedding <- nn_module(
+  initialize = function(head_dim, max_pos, base, factor, beta_fast, beta_slow,
+                        original_max_pos, mscale, mscale_all_dim) {
+    self$head_dim <- head_dim
+    self$max_pos <- max_pos
+    self$base <- base
+    self$factor <- factor
+    self$beta_fast <- beta_fast
+    self$beta_slow <- beta_slow
+    self$original_max_pos <- original_max_pos
+    self$mscale <- mscale
+    self$mscale_all_dim <- mscale_all_dim
+    self$cached_embeddings()
+  },
+  .load_from_state_dict = function(...) {
+    super$.load_from_state_dict(...)
+    self$cached_embeddings(invalidate = TRUE)
+  },
+ get_mscale = function(scale, mscale) {
+    if (mscale <= 0) return(1.0)
+    0.1 * mscale * log(scale) + 1.0
+  },
+  cached_embeddings = function(t = 1, invalidate = FALSE) {
+    invalidate <- invalidate || is.null(self$cos)
+    if (invalidate) {
+      dim <- self$head_dim
+      pos_freqs <- self$base ^ (torch_arange(0, dim - 1, step = 2) / dim)
+      inv_freq_extrapolation <- 1.0 / pos_freqs
+      inv_freq_interpolation <- 1.0 / (self$factor * pos_freqs)
+
+      c(low, high) %<-% yarn_find_correction_range(
+        self$beta_slow, self$beta_fast, dim, self$base, self$original_max_pos
+      )
+      inv_freq_extrapolation_factor <- yarn_linear_ramp_mask(low, high, dim / 2)
+
+      inv_freq <- inv_freq_interpolation * (1 - inv_freq_extrapolation_factor) +
+                  inv_freq_extrapolation * inv_freq_extrapolation_factor
+      self$inv_freq <- nn_buffer(inv_freq, persistent = FALSE)
+
+      self$attention_scale <- self$get_mscale(self$factor, self$mscale) /
+                              self$get_mscale(self$factor, self$mscale_all_dim)
+
+      freqs <- torch_arange(start = 0, end = self$max_pos - 1)$
+        float()$outer(self$inv_freq)$view(c(1, 1, self$max_pos, dim / 2))
+      emb <- torch_cat(list(freqs, freqs), dim = -1)
+      self$cos <- nn_buffer(emb$cos(), persistent = FALSE)
+      self$sin <- nn_buffer(emb$sin(), persistent = FALSE)
+    }
+    list(self$cos[,,1:t,], self$sin[,,1:t,], self$attention_scale)
+  },
+  forward = function(x) {
+    c(b, nh, t, ed) %<-% x$shape
+    c(cos, sin, attn_scale) %<-% self$cached_embeddings(t)
+    (x * cos + ministral_rotate_half(x) * sin) * attn_scale
+  }
+)
+
+nn_ministral_attention <- nn_module(
+  initialize = function(n_embd, n_head, n_kv_head, head_dim, max_pos,
+                        rope_base, rope_factor, rope_beta_fast, rope_beta_slow,
+                        rope_original_max_pos, rope_mscale, rope_mscale_all_dim) {
+    self$n_head <- n_head
+    self$n_kv_head <- n_kv_head
+    self$head_dim <- head_dim
+    self$n_kv_groups <- n_head %/% n_kv_head
+    self$max_pos <- max_pos
+
+    self$rotary <- nn_ministral_yarn_rotary_embedding(
+      head_dim, max_pos, rope_base, rope_factor, rope_beta_fast, rope_beta_slow,
+      rope_original_max_pos, rope_mscale, rope_mscale_all_dim
+    )
+
+    self$q_proj <- nn_linear(n_embd, n_head * head_dim, bias = FALSE)
+    self$k_proj <- nn_linear(n_embd, n_kv_head * head_dim, bias = FALSE)
+    self$v_proj <- nn_linear(n_embd, n_kv_head * head_dim, bias = FALSE)
+    self$o_proj <- nn_linear(n_head * head_dim, n_embd, bias = FALSE)
+    self$cached_bias()
+  },
+  forward = function(x) {
+    c(b, t, h) %<-% x$shape
+
+    q <- self$q_proj(x)$view(c(b, t, self$n_head, self$head_dim))$transpose(2, 3)
+    k <- self$k_proj(x)$view(c(b, t, self$n_kv_head, self$head_dim))$transpose(2, 3)
+    v <- self$v_proj(x)$view(c(b, t, self$n_kv_head, self$head_dim))$transpose(2, 3)
+
+    q <- self$rotary(q)$to(dtype = "float")
+    k <- self$rotary(k)$to(dtype = "float")
+
+    k <- repeat_kv(k, self$n_kv_groups)
+    v <- repeat_kv(v, self$n_kv_groups)
+
+    att <- torch_matmul(q, k$transpose(-2, -1)) * (1 / sqrt(self$head_dim))
+    att <- att$masked_fill(self$bias[,,1:t, 1:t] == 0, self$masked_bias)
+    att <- nnf_softmax(att, dim = -1)$to(dtype = v$dtype)
+
+    y <- torch_matmul(att, v)$transpose(2, 3)$contiguous()$
+      view(c(b, t, self$n_head * self$head_dim))
+    self$o_proj(y)
+  },
+  .load_from_state_dict = function(...) {
+    super$.load_from_state_dict(...)
+    self$cached_bias()
+  },
+  cached_bias = function() {
+    self$bias <- torch_ones(self$max_pos, self$max_pos)$bool()$tril()$
+      view(c(1, 1, self$max_pos, self$max_pos)) |> nn_buffer(persistent = FALSE)
+    self$masked_bias <- nn_buffer(torch_scalar_tensor(-Inf), persistent = FALSE)
+  }
+)
+
+nn_ministral_mlp <- nn_module(
+  initialize = function(n_embd, n_inter) {
+    self$gate_proj <- nn_linear(n_embd, n_inter, bias = FALSE)
+    self$down_proj <- nn_linear(n_inter, n_embd, bias = FALSE)
+    self$up_proj <- nn_linear(n_embd, n_inter, bias = FALSE)
+    self$act <- nn_silu()
+  },
+  forward = function(x) {
+    self$down_proj(self$act(self$gate_proj(x)) * self$up_proj(x))
+  }
+)
+
+nn_ministral_layer <- nn_module(
+  initialize = function(n_embd, n_inter, n_head, n_kv_head, head_dim, max_pos,
+                        rmsnorm_eps, rope_base, rope_factor, rope_beta_fast,
+                        rope_beta_slow, rope_original_max_pos, rope_mscale,
+                        rope_mscale_all_dim) {
+    self$ln_1 <- nn_ministral_rmsnorm(n_embd, rmsnorm_eps)
+    self$ln_2 <- nn_ministral_rmsnorm(n_embd, rmsnorm_eps)
+    self$attn <- nn_ministral_attention(
+      n_embd, n_head, n_kv_head, head_dim, max_pos, rope_base, rope_factor,
+      rope_beta_fast, rope_beta_slow, rope_original_max_pos, rope_mscale,
+      rope_mscale_all_dim
+    )
+    self$mlp <- nn_ministral_mlp(n_embd, n_inter)
+  },
+  forward = function(x) {
+    x <- x + self$attn(self$ln_1(x))
+    x + self$mlp(self$ln_2(x))
+  }
+)
+
+nn_ministral_model <- nn_module(
+  initialize = function(vocab_size, n_embd, n_inter, n_head, n_kv_head, head_dim,
+                        n_layer, max_pos, rmsnorm_eps, rope_base, rope_factor,
+                        rope_beta_fast, rope_beta_slow, rope_original_max_pos,
+                        rope_mscale, rope_mscale_all_dim) {
+    self$transformer <- nn_module_dict(list(
+      wte = nn_embedding(vocab_size, n_embd),
+      h = nn_sequential(!!!map(
+        1:n_layer,
+        \(x) nn_ministral_layer(
+          n_embd, n_inter, n_head, n_kv_head, head_dim, max_pos, rmsnorm_eps,
+          rope_base, rope_factor, rope_beta_fast, rope_beta_slow,
+          rope_original_max_pos, rope_mscale, rope_mscale_all_dim
+        )
+      )),
+      ln_f = nn_ministral_rmsnorm(n_embd, rmsnorm_eps)
+    ))
+    self$lm_head <- nn_linear(n_embd, vocab_size, bias = FALSE)
+  },
+  forward = function(idx) {
+    x <- self$transformer$wte(idx)
+    x <- self$transformer$h(x)
+    x <- self$transformer$ln_f(x)
+    self$lm_head(x)
+  }
+)
+
+#' ministral
+#'
+#' Initializes a Ministral-like model with YaRN RoPE and GQA
+#'
+#' @param vocab_size Vocabulary size.
+#' @param n_embd Embedding dimension.
+#' @param n_inter Intermediate size in MLP.
+#' @param n_head Number of attention heads.
+#' @param n_kv_head Number of key/value heads (for GQA).
+#' @param head_dim Dimension of each attention head.
+#' @param n_layer Number of transformer layers.
+#' @param max_pos Maximum position embeddings.
+#' @param rmsnorm_eps Epsilon for RMSNorm.
+#' @param rope_base Base for rotary embeddings.
+#' @param rope_factor YaRN scaling factor.
+#' @param rope_beta_fast YaRN beta_fast parameter.
+#' @param rope_beta_slow YaRN beta_slow parameter.
+#' @param rope_original_max_pos Original max position embeddings for YaRN.
+#' @param rope_mscale YaRN mscale parameter.
+#' @param rope_mscale_all_dim YaRN mscale_all_dim parameter.
+#' @param identifier HuggingFace model identifier.
+#' @param revision HuggingFace model revision.
+#' @returns An initialized [torch::nn_module()].
+#' @export
+ministral <- function(vocab_size = 131072, n_embd = 5120, n_inter = 16384,
+                      n_head = 32, n_kv_head = 8, head_dim = 128, n_layer = 40,
+                      max_pos = 262144, rmsnorm_eps = 1e-5, rope_base = 1e9,
+                      rope_factor = 16, rope_beta_fast = 32, rope_beta_slow = 1,
+                      rope_original_max_pos = 16384, rope_mscale = 1,
+                      rope_mscale_all_dim = 1) {
+  nn_ministral_model(
+    vocab_size, n_embd, n_inter, n_head, n_kv_head, head_dim, n_layer, max_pos,
+    rmsnorm_eps, rope_base, rope_factor, rope_beta_fast, rope_beta_slow,
+    rope_original_max_pos, rope_mscale, rope_mscale_all_dim
+  )
+}
+
+#' @describeIn ministral Initializes from HuggingFace config
+#' @export
+ministral_from_config <- function(identifier, revision = "main") {
+  path <- hfhub::hub_download(identifier, "config.json", revision = revision)
+  config <- jsonlite::fromJSON(path)
+
+  # Handle multimodal config (text_config nested)
+  if (!is.null(config$text_config)) {
+    rope_params <- config$text_config$rope_parameters
+    config <- config$text_config
+  } else {
+    rope_params <- config$rope_parameters %||% config
+  }
+
+  if (!config$model_type %in% c("ministral3", "mistral"))
+    cli::cli_abort("Unsupported model_type: {.val {config$model_type}}")
+
+  if (config$hidden_act != "silu")
+    cli::cli_abort("Unsupported hidden_act: {.val {config$hidden_act}}")
+
+  ministral(
+    vocab_size = config$vocab_size,
+    n_embd = config$hidden_size,
+    n_inter = config$intermediate_size,
+    n_head = config$num_attention_heads,
+    n_kv_head = config$num_key_value_heads,
+    head_dim = config$head_dim %||% (config$hidden_size %/% config$num_attention_heads),
+    n_layer = config$num_hidden_layers,
+    max_pos = config$max_position_embeddings,
+    rmsnorm_eps = config$rms_norm_eps %||% 1e-5,
+    rope_base = rope_params$rope_theta %||% 1e9,
+    rope_factor = rope_params$factor %||% 16,
+    rope_beta_fast = rope_params$beta_fast %||% 32,
+    rope_beta_slow = rope_params$beta_slow %||% 1,
+    rope_original_max_pos = rope_params$original_max_position_embeddings %||% 16384,
+    rope_mscale = rope_params$mscale %||% 1,
+    rope_mscale_all_dim = rope_params$mscale_all_dim %||% 1
+  )
+}
+
+#' @describeIn ministral Initializes and loads pretrained weights from HF Hub
+#' @export
+ministral_from_pretrained <- function(identifier, revision = "main") {
+  with_device(device = "meta", {
+    model <- ministral_from_config(identifier, revision)
+  })
+  state_dict <- hf_state_dict(identifier, revision)
+  state_dict <- ministral_hf_weights_remap(state_dict)
+  model$load_state_dict(state_dict, .refer_to_state_dict = TRUE)
+  model
+}
+
+ministral_hf_weights_remap <- function(state_dict) {
+  nms <- names(state_dict)
+
+  # Handle multimodal models (language_model prefix)
+  nms <- gsub("^language_model\\.", "", nms)
+
+  # Standard remapping
+  nms <- gsub("model.embed_tokens.weight", "transformer.wte.weight", nms, fixed = TRUE)
+  nms <- gsub("model.layers", "transformer.h", nms, fixed = TRUE)
+  nms <- gsub("self_attn", "attn", nms, fixed = TRUE)
+  nms <- gsub("input_layernorm", "ln_1", nms, fixed = TRUE)
+  nms <- gsub("post_attention_layernorm", "ln_2", nms, fixed = TRUE)
+  nms <- gsub("model.norm", "transformer.ln_f", nms, fixed = TRUE)
+
+  names(state_dict) <- nms
+
+  # Filter out non-language model weights
+  keep <- !grepl("vision_tower|multi_modal_projector|scale", names(state_dict))
+  state_dict[keep]
+}