Problem Set 06: Growth and parameter inference

ASTR 476: Observational Cosmology · 2026-09-25

Scope: Lectures 11-12. Four questions; submit derivations and code/output where requested.

State units and model assumptions. Keep unrounded values in code and round only in your final communication. Revisions and resubmissions are encouraged.

Question 1

Report the normalized model growth factor at z=0, 0.5, and 1 from the supplied script. Describe the normalization and two omitted physical effects.

Work to show: equations, units, assumptions, and a reproducible computation where requested.

Question 2

Estimate f=d ln D/d ln a at z=0.5 with centered finite differences using h=0.01 and h=0.005. Compare the results and state a convergence criterion.

Work to show: equations, units, assumptions, and a reproducible computation where requested.

Question 3

For a Gaussian residual vector, derive the Cholesky-whitened expression for chi-square and explain why explicit matrix inversion is discouraged.

Work to show: equations, units, assumptions, and a reproducible computation where requested.

Question 4

Distinguish a likelihood contour from a marginalized posterior contour. Name one way a prior can affect the latter.

Work to show: equations, units, assumptions, and a reproducible computation where requested.

ASTR 476 · Problem Set 06 · 2026-09-25