Remove MPI dependency, replace with single-process stub for non-MPI builds

- Add mpi_stub.h providing all MPI types/constants/functions as no-ops
  (nprocs=1, myrank=0) with memcpy-based Allreduce and clock_gettime Wtime
- Replace #include <mpi.h> with conditional #ifdef MPI_STUB in 31 files
  (19 headers + 12 source files) preserving ability to build with real MPI
- Change makefile.inc: CLINKER mpiicpx->icpx, add -DMPI_STUB to CXXAPPFLAGS
- Update makefile_and_run.py: run ./ABE directly instead of mpirun -np N
- Set MPI_processes=1 in AMSS_NCKU_Input.py

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

AMSS_NCKU_source/mpi_stub.h

@@ -0,0 +1,153 @@
+#ifndef MPI_STUB_H
+#define MPI_STUB_H
+
+/*
+ * MPI Stub Header — single-process shim for AMSS-NCKU ABE solver.
+ * Provides all MPI types, constants, and functions used in the codebase
+ * as no-ops or trivial implementations for nprocs=1, myrank=0.
+ */
+
+#include <cstring>
+#include <cstdlib>
+#include <cstdio>
+#include <time.h>
+
+/* ── Types ─────────────────────────────────────────────────────────── */
+
+typedef int MPI_Comm;
+typedef int MPI_Datatype;
+typedef int MPI_Op;
+typedef int MPI_Request;
+typedef int MPI_Group;
+
+typedef struct MPI_Status {
+    int MPI_SOURCE;
+    int MPI_TAG;
+    int MPI_ERROR;
+} MPI_Status;
+
+/* ── Constants ─────────────────────────────────────────────────────── */
+
+#define MPI_COMM_WORLD  0
+
+#define MPI_INT              1
+#define MPI_DOUBLE           2
+#define MPI_DOUBLE_PRECISION 2
+#define MPI_DOUBLE_INT       3
+
+#define MPI_SUM    1
+#define MPI_MAX    2
+#define MPI_MAXLOC 3
+
+#define MPI_STATUS_IGNORE   ((MPI_Status *)0)
+#define MPI_STATUSES_IGNORE ((MPI_Status *)0)
+
+#define MPI_MAX_PROCESSOR_NAME 256
+
+/* ── Helper: sizeof for MPI_Datatype ──────────────────────────────── */
+
+static inline size_t mpi_stub_sizeof(MPI_Datatype type) {
+    switch (type) {
+        case MPI_INT:        return sizeof(int);
+        case MPI_DOUBLE:     return sizeof(double);
+        case MPI_DOUBLE_INT: return sizeof(double) + sizeof(int);
+        default:             return 0;
+    }
+}
+
+/* ── Init / Finalize ──────────────────────────────────────────────── */
+
+static inline int MPI_Init(int *, char ***) { return 0; }
+static inline int MPI_Finalize() { return 0; }
+
+/* ── Communicator queries ─────────────────────────────────────────── */
+
+static inline int MPI_Comm_rank(MPI_Comm, int *rank) { *rank = 0; return 0; }
+static inline int MPI_Comm_size(MPI_Comm, int *size) { *size = 1; return 0; }
+static inline int MPI_Comm_split(MPI_Comm comm, int, int, MPI_Comm *newcomm) {
+    *newcomm = comm;
+    return 0;
+}
+static inline int MPI_Comm_free(MPI_Comm *) { return 0; }
+
+/* ── Group operations ─────────────────────────────────────────────── */
+
+static inline int MPI_Comm_group(MPI_Comm, MPI_Group *group) {
+    *group = 0;
+    return 0;
+}
+static inline int MPI_Group_translate_ranks(MPI_Group, int n,
+        const int *ranks1, MPI_Group, int *ranks2) {
+    for (int i = 0; i < n; ++i) ranks2[i] = ranks1[i];
+    return 0;
+}
+static inline int MPI_Group_free(MPI_Group *) { return 0; }
+
+/* ── Collective operations ────────────────────────────────────────── */
+
+static inline int MPI_Allreduce(const void *sendbuf, void *recvbuf,
+        int count, MPI_Datatype datatype, MPI_Op, MPI_Comm) {
+    std::memcpy(recvbuf, sendbuf, count * mpi_stub_sizeof(datatype));
+    return 0;
+}
+
+static inline int MPI_Iallreduce(const void *sendbuf, void *recvbuf,
+        int count, MPI_Datatype datatype, MPI_Op, MPI_Comm,
+        MPI_Request *request) {
+    std::memcpy(recvbuf, sendbuf, count * mpi_stub_sizeof(datatype));
+    *request = 0;
+    return 0;
+}
+
+static inline int MPI_Bcast(void *, int, MPI_Datatype, int, MPI_Comm) {
+    return 0;
+}
+
+static inline int MPI_Barrier(MPI_Comm) { return 0; }
+
+/* ── Point-to-point (never reached with nprocs=1) ─────────────────── */
+
+static inline int MPI_Send(const void *, int, MPI_Datatype, int, int, MPI_Comm) {
+    return 0;
+}
+static inline int MPI_Recv(void *, int, MPI_Datatype, int, int, MPI_Comm, MPI_Status *) {
+    return 0;
+}
+static inline int MPI_Isend(const void *, int, MPI_Datatype, int, int, MPI_Comm,
+        MPI_Request *req) {
+    *req = 0;
+    return 0;
+}
+static inline int MPI_Irecv(void *, int, MPI_Datatype, int, int, MPI_Comm,
+        MPI_Request *req) {
+    *req = 0;
+    return 0;
+}
+
+/* ── Completion ───────────────────────────────────────────────────── */
+
+static inline int MPI_Wait(MPI_Request *, MPI_Status *) { return 0; }
+static inline int MPI_Waitall(int, MPI_Request *, MPI_Status *) { return 0; }
+
+/* ── Utility ──────────────────────────────────────────────────────── */
+
+static inline int MPI_Abort(MPI_Comm, int error_code) {
+    std::fprintf(stderr, "MPI_Abort called with error code %d\n", error_code);
+    std::exit(error_code);
+    return 0;
+}
+
+static inline double MPI_Wtime() {
+    struct timespec ts;
+    clock_gettime(CLOCK_MONOTONIC, &ts);
+    return (double)ts.tv_sec + (double)ts.tv_nsec * 1.0e-9;
+}
+
+static inline int MPI_Get_processor_name(char *name, int *resultlen) {
+    const char *stub_name = "localhost";
+    std::strcpy(name, stub_name);
+    *resultlen = (int)std::strlen(stub_name);
+    return 0;
+}
+
+#endif /* MPI_STUB_H */