more things to prove
derivations? why are my matrices not conforooooororrming
plan.txt
I seem to have found a bug: the way it's phrased, we get V = ULUL or LULU which has no particularly efficient method to compute with..
more proofs
noooooooooo, this line was very wrong. proof-by-computer shows the new one is correct.

This is the proof by computer:
a=20000; b=10; X = rnorm(a*b); dim(X) = c(a,b); S=t(X)%*%X; norm(chol(solve(S)) - solve(chol(S)))
run it enough times and vary a and b and tell me the chance that this theorem is wrong.
notes
Basic timing tests for different Ax=b solvers.
Sparse tests are strange. Now I am tired.