Log in Start free

Counterexample bank

Part C is won by knowing which tempting claims are false. 148 counterexamples; 85 free. The rest come with the Notes pack.

All ODE PDE abelian analyticity anova baire calculus of variations canonical forms cauchy-riemann compactness completeness complex conformal connectedness continuity contour integration convergence differentiation distributions fields fixed point galois green groups harmonic injectivity integral equations integration laurent limsup linear algebra liouville lp markov measure mechanics metric spaces multivariable multivariate numerical p-groups permutations polynomials power series probability quadratic forms real analysis regression residues rings sampling separability separation sequences series singularities stability statistics sylow testing topology uniform convergence wronskian zeros

#1 · Probability & Statistics › Limit Theorems and Markov Chains

“An irreducible chain with a stationary distribution converges to it” — false

Counterexample: The two-state chain that swaps deterministically (period 2)

$π = ($ ½, ½) is stationary and unique, but $p_{nij}$ oscillates between 0 and 1. Aperiodicity is required.

probabilitymarkov

#2 · Probability & Statistics › Limit Theorems and Markov Chains

“A recurrent chain has a stationary distribution” — false

Counterexample locked — unlock with Notes + PYQ

probabilitymarkov