add unfinished part of 2024-11-27

2024-11-27-rest.md

@@ -0,0 +1,91 @@
+---
+marp: true
+theme: ginkgo
+headingDivider: 2
+---
+
+
+## Passing Data out of Ginkgo
+
+**Note:** Only possible as views.
+
+Examples for accessing the underlying pointer(s):
+
+- Array: `arr.get_data()`
+- Dense vector: `vec.get_values()`
+- CSR matrix: `mtx.get_row_ptrs()`, `mtx.get_col_idxs()`, `mtx.get_values()`
+
+
+## Example: Calling BLAS Routine with Ginkgo Data
+
+```c++
+auto x = gko::matrix::Dense<float>::create(exec, gko::dim<2>{n_row, 1});
+auto y = gko::matrix::Dense<float>::create(exec, gko::dim<2>{n_row, 1});
+
+cblas_srot(n_row, x->get_values(), x->get_stride(), y->get_values(), y->get_stride(),
+           cos, sin);
+
+```
+
+## Example: Passing Ginkgo Data to Kokkos
+
+Special case for passing data to Kokkos via `gko::ext::kokkos::map_data`.
+Works for `gko::array` and `gko::matrix::Dense`.
+
+```c++
+auto g_vec = gko::matrix::Dense<float>::create(exec, gko::dim<2>{n_row, 1});
+
+auto k_vec = gko::ext::kokkos::map_data(g_vec); // this is a 2D Kokkos::View
+Kokkos::parallel_for(
+  n_row, KOKKOS_LAMBDA(int i){           
+    const float h = 1.0f / (discretization_points + 1);
+    const float xi = ValueType(i + 1) * h;
+    k_vec[i] = xi * xi;
+  }
+);
+
+```
+
+# Advanced `gko::array<T>` Topics
+
+<!-- _class: lead -->
+
+
+
+## Cross Executor Copy and Move
+
+Scenario: copy construct (assign) arrays with different executors
+
+```c++
+auto cpu_exec = gko::OmpExecutor::create();
+auto gpu_exec = gko::CudaExecutor::create(0, cpu_exec);
+
+gko::array<int> arr_cpu(cpu_exec, ...);
+gko::array<int> arr_gpu(gpu_exec);
+
+arr_gpu = arr_cpu;
+```
+
+The data will be automatically copied between the CPU and GPU.
+
+Using `arr_gpu = std::move(arr_cpu)` involves a copy instead of a move.
+
+
+**Note:** `gko::array<int> arr_gpu(arr_cpu)` will create `arr_gpu` using the executor from `arr_cpu`.
+
+
+## Executor behavior
+
+The executor *doesn't* change implicitly.
+After assignment `arr_a = arr_b` the executor of `arr_a` will be *the same as before* the assignment.
+The same holds for move assignments.
+
+Explicitly change executor with `arr.set_executor(other_exec)`
+
+**Exceptions:**
+When `arr_a` was *default constructed*, the assignment changes the executor.
+
+
+
+Default constructed array has no executor
+Change executor with `array.set_executor(other_exec)`