simple_debug.cpp

#include <iostream>
#include <vector>

// LAPACK function
extern "C" {
    void dpotrf_(const char* uplo, const int* n, double* a, const int* lda, int* info);
}

int main() {
    std::cout << "Testing basic LAPACK Cholesky on identity matrix\n";
    
    // 2x2 identity matrix in column-major order
    int n = 2;
    double matrix[4] = {1.0, 0.0, 0.0, 1.0};  // column-major: [1,0; 0,1]
    
    std::cout << "Original matrix (column-major):\n";
    std::cout << matrix[0] << " " << matrix[2] << "\n";
    std::cout << matrix[1] << " " << matrix[3] << "\n";
    
    int info;
    dpotrf_("U", &n, matrix, &n, &info);
    
    std::cout << "After Cholesky factorization, info = " << info << "\n";
    std::cout << "Factorized matrix:\n";
    std::cout << matrix[0] << " " << matrix[2] << "\n";
    std::cout << matrix[1] << " " << matrix[3] << "\n";
    
    if (info == 0) {
        std::cout << "SUCCESS: Cholesky factorization worked\n";
    } else {
        std::cout << "FAILED: Cholesky factorization failed with info = " << info << "\n";
    }
    
    return 0;
}