feat: initial release

Assisted-by: GLM 5.3 Flash

grad/permute.go

@@ -0,0 +1,42 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: MIT
+
+package grad
+
+import (
+	"sourcedock.dev/petrbalvin/tensor/internal/core"
+)
+
+// TransposeAxes reorders the axes of a tensor by dims. The backward
+// applies the inverse permutation to the incoming gradient: axis moves
+// are invertible data motion, so no element mixing occurs and the
+// gradient is exactly the same move played backwards.
+func (t *Tensor) TransposeAxes(dims ...int) (*Tensor, error) {
+	if err := t.checkDiff("TransposeAxes"); err != nil {
+		return nil, err
+	}
+	out, err := core.TransposeAxes(t.data, dims...)
+	if err != nil {
+		return nil, err
+	}
+	perm := append([]int(nil), dims...)
+	orig := t.data.Shape()
+	return t.unaryResult("TransposeAxes", out, func(g gradSlot, dst *[2]gradSlot, ar *gradArena) error {
+		dx, err := core.TransposeAxes(g.arr, inversePerm(perm)...)
+		if err != nil {
+			return err
+		}
+		dst[0] = gradSlot{arr: dx, sh: orig}
+		return nil
+	}), nil
+}
+
+// inversePerm flips an axis permutation: if out = permute(x, p), then
+// permute(out, p⁻¹) restores x's axis order.
+func inversePerm(perm []int) []int {
+	inv := make([]int, len(perm))
+	for i, p := range perm {
+		inv[p] = i
+	}
+	return inv
+}