Update notes.md

Processor and RAM considerations.

notes.md

@@ -57,4 +57,49 @@
 
 * toolset vs. builtin - e.g. is building network a tool in the toolset or a function in the model setup?
 * relationship w/calibration
-* 
+
+## Technicalities
+
+|Minimal Payload|bytes|
+|---------------|:---:|
+| immune status (T/F) | 1 |
+| infectious timer (\< 256 days) | 1 |
+| &Sigma; | **2** |
+
+|Realistic Payload|bytes|
+|-----------------|:---:|
+| age of DoB (115 years = 41,975 days) | 2 |
+| susceptibility (would use float16 on GPU) | 4 |
+| accessibility | 1 |
+| SES/nutrition status | 1 |
+| exposed timer (\< 256 days) | 1 |
+| infectious timer (\< 256 days) | 1 |
+| age at infection | 2 |
+| community ID (up to 65K communities) | 2 |
+| &Sigma; | **14** |
+
+|Population|Minimal Payload<br>(2 bytes)|Minimally Realistic<br>Payload (14 bytes)|CPAS*|pass/sec†|notes|
+|:--------:|:---------------------:|:---------------:|:-:|:-:|:-:|
+|1M  (10<sup>6</sup>)|2MB|14MB|2,000|23,000/~3,300||
+|10M (10<sup>7</sup>)|20MB|140MB|200|2,300/~330|megacity|
+|100M (10<sup>8</sup>)|200MB|1.4GB|20|230/~33||
+|200M (2x10<sup>8</sup>)|400MB|2.8GB|10|115/~16|Nigeria (231M)<br>Pakistan (242M)|
+|1G (10<sup>9</sup>)|2GB|14GB|2|23/~3.3||
+
+*CPAS - cycles/agent/second (2GHz CPU). SIMD instructions could be a multiplier on the number of instructions/cycle, e.g. AVX on Intel with 256-bit registers can operate on 8 float32s simultaneously. Apple Silicon supports ARM NEON with 128-bit registers.
+
+†How many passes over memory/second based on memory bandwidth (Lenovo ~46GB/s, Apple Silicon up to 800GB/s).
+
+### PRNG State Considerations
+
+PRNG state appears to use between 16 and 268 bytes depending on the algorithm. CPU based modeling can probably allocate state for each CPU code in use (vanishingly small memory use). GPU based modeling will probably need to group agents to use draws from a shared PRNG to amortize the memory usage across several agents. E.g., 16 agents using the same PRNG with 16 bytes of state only incur +1 byte of state/agent.
+
+|Algorithm|State Size (bytes)|
+|:--------|:----------------:|
+|XOROSHIRO128+| 16 |
+|other XOROSHIRO variations| 16+ |
+|XORWOW| 44 |
+|MRG32k3a| 44 |
+|Sobel32| 140 |
+|Sobel64| 268 |
+