# Quantum Bayesian Networks

## April 25, 2009

### I, Grammaticus, speak about simulation

Filed under: Uncategorized — rrtucci @ 6:29 am

(Grammaticus=the Grammarian)

From time to time, I, Grammaticus, Caesar of the vast Roman Empire, will compare the way base humans say something to the way divine Caesar does. In a previous blog post, Grammaticus compared the Quayle (HUMAN) convention to the Dirac (DIVINE) convention for quantum circuit diagrams. In this blog post, Grammaticus addresses the use of the word simulation.

Definitions from The American Heritage Dictionary. Use of boldface is by Grammaticus.

sim·u·late
tr.v. sim·u·lat·ed, sim·u·lat·ing, sim·u·lates
1.
a. To have or take on the appearance, form, or sound of; imitate.
b. To make in imitation of or as a substitute for. See Synonyms at imitate.
2. To make a pretense of; feign: simulate interest.
3. To create a representation or model of (a physical system or particular situation, for example).

com·pile
tr.v. com·piled, com·pil·ing, com·piles
1. To gather into a single book.
2. To put together or compose from materials gathered from several sources: compile an encyclopedia.
3. (Computer Science) To translate (a program) into machine language.

 How a base human speaks How Divine Grammaticus speaks This is a simulation of the weather or of zero gravity. Same, if what is meant is that an imitation (like a computer model) of the physical process is given. We simulated the Hamiltonian H. We simulated a unitary matrix $U=e^{-itH}$. (Examples of this base usage here and here.) Use this We compiled the Hamiltonian H or the unitary matrix $U=e^{-itH}$, either exactly or approximately. if what is meant is that the matrix H (or the matrix U) was expressed or decomposed, either approximately or exactly, into a sequence of elementary operators (SEO) which equals H (or U). Elementary operators are usually one or two qubit operators. A SEO is the machine language of quantum computers, so Grammaticus is here following standard usage by American Heritage and other muses, whereas base humans are redefining and defiling the language. Note that in the vile human usage, the word “simulation” corresponds most closely to “approximate compilation”. Thus, there is no word for “exact compilation” in the vile, limited language of mortals, unless you want to say “exact simulation”, which sounds like an ugly oxymoron to all nine muses. Thalia, the muse of comedy, points out that “The quantum GNU simulator” sounds like a nefarious “The Matrix” program, whereas “The quantum GNU compiler” sounds more familiar and thus less scary.