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Force rep_matrix to always return column-major matrices #3342

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Merged
andrjohns merged 1 commit into from
Jul 11, 2026
+15 −2
Merged

Force rep_matrix to always return column-major matrices #3342

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5 changes: 3 additions & 2 deletions stan/math/prim/fun/rep_matrix.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -47,11 +47,12 @@ inline auto rep_matrix(const T& x, int m, int n) {
* vector.
* @tparam Vec An Eigen vector.
* @param x An Eigen vector. For Row vectors the values are replicated rowwise.
* and for column vectors the values are repliacated colwise.
* and for column vectors the values are replicated colwise.
* @param n Number of rows or columns.
*/
template <typename Vec, require_eigen_vector_t<Vec>* = nullptr>
inline auto rep_matrix(const Vec& x, int n) {
inline Eigen::Matrix<scalar_type_t<Vec>, -1, -1> rep_matrix(const Vec& x,
int n) {
if constexpr (is_eigen_row_vector<Vec>::value) {
check_nonnegative("rep_matrix", "rows", n);
return x.replicate(n, 1);
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12 changes: 12 additions & 0 deletions test/unit/math/prim/fun/rep_matrix_test.cpp
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Expand Up @@ -52,3 +52,15 @@ TEST(MathMatrixPrimMat, rep_matrix_row_vec) {

EXPECT_THROW(rep_matrix(rv, -1), std::domain_error);
}

TEST(MathMatrixPrimMat, rep_matrix_both_ways) {
using stan::math::rep_matrix;

Eigen::Matrix<double, 1, Eigen::Dynamic> rv(3);
rv << 1.0, 4.0, 9.0;

Eigen::Matrix<double, Eigen::Dynamic, 1> v(3);
v << 1.0, 4.0, 9.0;
Eigen::Matrix<double, Eigen::Dynamic, Eigen::Dynamic> x(3, 3);
x = true ? rep_matrix(v, 3) : rep_matrix(rv, 3);
}