Fix some content

1-4-scalability.md

@@ -58,7 +58,7 @@
 
 - formula
     - Speedup factor:
-      $$S = T / (\alpha \times T + (1 - \alpha \times T / n)) = 1 / (\alpha + (1 - \alpha) / n)$$
+      $$S = T / (\alpha \times T + (1 - \alpha) \times T / n) = 1 / (\alpha + (1 - \alpha) / n)$$
     - $\alpha$: fraction of serial computation
     - 1 - alpha: part that can be parallelized
     - $n$: processors used

2-2-cuda.md

@@ -44,7 +44,7 @@
     ```
 - Note to self: run `nvcc` with `-arch=native` otherwise it won't work.
 
-### Device code and Host code
+### Device code and Host code (Important)
 
 - Compiler `nvcc` separates source code into host and device code
     - Device code (kernels): definition marked with `__global__`, called from