# Convert a DAG to a CPDAG Convert a DAG (Directed Acyclic Graph) to a Completed Partially Directed Acyclic Graph (CPDAG). ```r dag2cpdag(g) ``` ## Arguments - `g`: an object of class `"graph"` (package `graph`), representing a DAG. ## Details This function converts a DAG into its corresponding (unique) CPDAG as follows. Because every DAG in the Markov equivalence class described by a CPDAG shares the same skeleton and the same v-structures, this function takes the skeleton and the v-structures of the given DAG `g`. Afterwards it simply uses the 3 orientation rules of the PC algorithm (see references) to orient as many of the remaining undirected edges as possible. The function is a simple wrapper function for `dag2essgraph` which is more powerfull since it also allows the calculation of the Markov equivalence class in the presence of interventional data. The output of this function is exactly the same as the one using ``` pc(suffStat, indepTest, alpha, labels) ``` using the true correlation matrix in the function `gaussCItest` with a large virtual sample size and a large alpha, but it is much faster. ## Returns A graph object containing the CPDAG. ## References C. Meek (1995). Causal inference and causal explanation with background knowledge. In **Proceedings of the Eleventh Conference on Uncertainty in Artificial Intelligence (UAI-95)**, pp. 403-411. Morgan Kaufmann Publishers, Inc. P. Spirtes, C. Glymour and R. Scheines (2000) **Causation, Prediction, and Search**, 2nd edition, The MIT Press. ## Author(s) Markus Kalisch (kalisch@stat.math.ethz.ch ) and Alain Hauser(alain.hauser@bfh.ch ) ## See Also `dag2essgraph`, `randomDAG`, `pc` ## Examples ```r ## A -> B <- C am1 <- matrix(c(0,1,0, 0,0,0, 0,1,0), 3,3) colnames(am1) <- rownames(am1) <- LETTERS[1:3] g1 <- as(t(am1), "graphNEL") ## convert to graph cpdag1 <- dag2cpdag(g1) if(requireNamespace("Rgraphviz")) { par(mfrow = c(1,2)) plot(g1) plot(cpdag1) } ## A -> B -> C am2 <- matrix(c(0,1,0, 0,0,1, 0,0,0), 3,3) colnames(am2) <- rownames(am2) <- LETTERS[1:3] g2 <- as(t(am2), "graphNEL") ## convert to graph cpdag2 <- dag2cpdag(g2) if(requireNamespace("Rgraphviz")) { par(mfrow = c(1,2)) plot(g2) plot(cpdag2) } ```

dag2cpdag function