# E068: Dirichlet L(s,χ): series vs. Euler product (partial approximations).

```{figure} ../_static/experiments/e068_hero.png
:width: 80%
:alt: Preview figure for E068
```

**Tags:** `number-theory`, `quantitative-exploration`, `visualization`, `dirichlet-characters`, `l-functions`

## Highlights
- Computes truncated Dirichlet L-series for a nontrivial character.
- Compares series truncation against Euler-product truncation (where meaningful).
- Shows convergence behavior (fast for s>1, slow at s=1).

## What this experiment does

For Re(s) > 1, Dirichlet L-functions admit both:

The implementation focuses on a compact, reproducible numerical workflow: deterministic parameter defaults, structured output folders, and one or more figures saved for the gallery.

## Outputs

This experiment writes into `out/e068/`:

- `figures/fig_01_series_vs_euler.png`

## How to run

```bash
make run EXP=e068
```

## Notes

- The gallery preview figure shipped with the documentation uses conservative cutoffs so builds stay fast. If you run the experiment locally, increase the cutoffs to see the asymptotic regime more clearly.
- Prime-race plots depend on the chosen sampling of `x` (linear vs. log grid). The qualitative “who leads” picture can change when you zoom in.

## Published run snapshot

If this experiment is included in the docs gallery, include the published snapshot (report + params).

```{include} ../reports/e068.md
:start-after: "<!-- REPORT:BEGIN -->"
:end-before: "<!-- REPORT:END -->"
```

::: {dropdown} params.json (snapshot)
:open:

```{literalinclude} ../params/e068.json
:language: json
```

:::

## References

{cite:t}`apostol1976introanalyticnumbertheory, montgomeryvaughan2006multiplicativenumbertheoryi`

## Related experiments

- {doc}`e111` (E111: Euler product vs. Dirichlet series for L(s,χ))
- {doc}`e110` (E110: Dirichlet L-series partial sums at s=1 and s=1/2)
- {doc}`e083` (E083: Series vs. Euler product (ζ))
- {doc}`e091` (E091: Partial Euler products on the critical line)
- {doc}`e092` (E092: 1/ζ(s) via the Möbius Dirichlet series)