---
title: "Getting Started with PFCI"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Getting Started with PFCI}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r setup, include = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)
```

## Overview

The `PFCI` package implements **Penalized Fast Causal Inference**, a two-stage
procedure for learning causal structure in high-dimensional settings with
potential latent variables and selection bias. The method combines graphical
lasso screening with the FCI algorithm to produce a Partial Ancestral Graph
(PAG) that is substantially faster than standard FCI/RFCI while maintaining
accuracy under sparsity.

## Installation

`PFCI` is available on CRAN. It requires `pcalg` and `graph` from Bioconductor
for its core functionality:

## Basic workflow

The standard three-step workflow is simulate, fit, evaluate:

```{r basic, eval = FALSE}
library(PFCI)

# Step 1: simulate a sparse DAG with p = 100 nodes
sim <- simulate_pfci_toy(p = 100, n = 100, edge_prob = 0.02, seed = 1)

# Step 2: fit PFCI
fit <- pfci_fit(sim$X, alpha = 0.05)
print(fit)

# Step 3: evaluate against ground truth
met <- pfci_metrics(sim, fit)
met
```

The `print(fit)` call reports runtime and tuning parameters. 
The `met` list contains SHD, F1, MCC, Precision, Recall, and Time.

## Plotting the PAG

```{r plot, eval = FALSE}
plot_pag(fit)
```

## Latent confounders

To simulate and evaluate under latent confounding use the
`simulate_with_latent` and `metrics_with_latent` functions:

```{r latent, eval = FALSE}
sim_lat <- simulate_with_latent(p_obs = 100, gamma = 0.05, n = 100,
                                seed_graph = 1, seed_data = 2)
fit_lat <- pfci_fit(sim_lat$X, alpha = 0.05)
metrics_with_latent(sim_lat, fit_lat)
```

## Scaling behaviour

PFCI is approximately 3x faster than RFCI at `p = 1000` while maintaining
equal or better F1 and MCC. See Table 1 of Pal, Ghosh, and Yang (2025) for
full simulation results across `p = 100` to `p = 1000`.

## Reference

Pal, S., Ghosh, D., and Yang, S. (2025). Penalized FCI for Causal Structure
Learning in a Sparse DAG for Biomarker Discovery in Parkinson's Disease.
*Annals of Applied Statistics*. <doi:10.48550/arXiv.2507.00173>
