# Kernel Execution
Kernels are GPU programs that operate on buffers.
## Running a Kernel
```elixir
{:ok, cmd_id} = ExCubecl.run_kernel(name, inputs, output, params \\ %{})
```
- `name` — string kernel name (see below)
- `inputs` — list of input buffer IDs
- `output` — output buffer ID
- `params` — optional map of kernel-specific parameters
## Available Kernels
```elixir
{:ok, kernels} = ExCubecl.kernels()
# ["elementwise_add", "elementwise_mul", "elementwise_sub",
# "elementwise_div", "relu", "sigmoid", "tanh", "matmul",
# "reduce_sum", "reduce_max", "reduce_min", "softmax",
# "layer_norm", "conv2d", "transpose", "reshape"]
```
## Element-wise Operations
```elixir
{:ok, a} = ExCubecl.buffer([1.0, 2.0, 3.0], [3], :f32)
{:ok, b} = ExCubecl.buffer([4.0, 5.0, 6.0], [3], :f32)
{:ok, output} = ExCubecl.buffer([0.0, 0.0, 0.0], [3], :f32)
{:ok, _cmd} = ExCubecl.run_kernel("elementwise_add", [a, b], output, %{})
{:ok, _cmd} = ExCubecl.run_kernel("elementwise_mul", [a, b], output, %{})
```
## Activation Functions
```elixir
{:ok, input} = ExCubecl.buffer([-1.0, 0.0, 1.0], [3], :f32)
{:ok, output} = ExCubecl.buffer([0.0, 0.0, 0.0], [3], :f32)
{:ok, _cmd} = ExCubecl.run_kernel("relu", [input], output, %{})
{:ok, _cmd} = ExCubecl.run_kernel("sigmoid", [input], output, %{})
{:ok, _cmd} = ExCubecl.run_kernel("tanh", [input], output, %{})
```
## Reductions
```elixir
{:ok, input} = ExCubecl.buffer([1.0, 5.0, 3.0, 2.0], [4], :f32)
{:ok, output} = ExCubecl.buffer([0.0], [1], :f32)
{:ok, _cmd} = ExCubecl.run_kernel("reduce_sum", [input], output, %{})
{:ok, _cmd} = ExCubecl.run_kernel("reduce_max", [input], output, %{})
{:ok, _cmd} = ExCubecl.run_kernel("reduce_min", [input], output, %{})
```
## Matrix Multiplication
```elixir
# 2x3 matrix
{:ok, a} = ExCubecl.buffer([1.0, 2.0, 3.0, 4.0, 5.0, 6.0], [2, 3], :f32)
# 3x2 matrix
{:ok, b} = ExCubecl.buffer([7.0, 8.0, 9.0, 10.0, 11.0, 12.0], [3, 2], :f32)
# Output: 2x2 matrix
{:ok, output} = ExCubecl.buffer(List.duplicate(0.0, 4), [2, 2], :f32)
{:ok, _cmd} = ExCubecl.run_kernel("matmul", [a, b], output, %{})
```
## Convolution
```elixir
# 1x3x3 input (batch=1, channels=1, 3x3 spatial)
{:ok, input} = ExCubecl.buffer([1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0],
[1, 1, 3, 3], :f32)
# 1x1x2x2 kernel
{:ok, kernel} = ExCubecl.buffer([1.0, 0.0, 0.0, -1.0], [1, 1, 2, 2], :f32)
{:ok, output} = ExCubecl.buffer(List.duplicate(0.0, 4), [1, 1, 2, 2], :f32)
{:ok, _cmd} = ExCubecl.run_kernel("conv2d", [input, kernel], output, %{})
```
## Shape Operations
```elixir
{:ok, input} = ExCubecl.buffer([1.0, 2.0, 3.0, 4.0], [4], :f32)
# Reshape to 2x2
{:ok, output} = ExCubecl.buffer(List.duplicate(0.0, 4), [2, 2], :f32)
{:ok, _cmd} = ExCubecl.run_kernel("reshape", [input], output, %{})
# Transpose
{:ok, transposed} = ExCubecl.buffer(List.duplicate(0.0, 4), [2, 2], :f32)
{:ok, _cmd} = ExCubecl.run_kernel("transpose", [output], transposed, %{})
```
## Custom Kernels (Phase 2+)
Custom CubeCL kernels can be registered at runtime. See the [CubeCL documentation](https://github.com/tracel-ai/cubecl) for kernel authoring.