Which MPI collective routine combines values from an array into a scalar result?MPI_GatherMPI_ReduceMPI_AllgatherMPI_Barrier

The MPI collective routine that combines values from an array into a scalar result is MPI_Reduce. This function applies a reduction operation (such as sum, product, logical AND/OR, min, max, etc.) on all processes within a communicator and returns the result to one process. The other options listed, MPI_Gather, MPI_Allgather, and MPI_Barrier, perform different functions. MPI_Gather collects individual data from each process and gathers them to the root process. MPI_Allgather does the same but sends the gathered data to all processes. MPI_Barrier is a synchronization routine that blocks the caller until all processes in the communicator have called it.