Update pypolymlp interface documentation

doc/pypolymlp.md

@@ -257,12 +257,13 @@ corresponding forces are stored in the `phono3py_mlp_eval_dataset` file.
 After developing MLPs, random displacements are generated by specifying
 {ref}`--rd <random_displacements_option>` option. To compute force constants
 with random displacements, an external force constants calculator is necessary.
-For this, symfc is used which is invoked by `--symfc` option.
+By default, symfc is used unless another force constants solver is explicitly
+specified.
 
 Having `phono3py_params.yaml`, phono3py is executed with `--pypolymlp` option,
 
 ```
-% phono3py-load --pypolymlp --rd 200 --symfc phono3py_params.yaml
+% phono3py-load --pypolymlp --rd 200 phono3py_params.yaml
         _                      _____
   _ __ | |__   ___  _ __   ___|___ / _ __  _   _
  | '_ \| '_ \ / _ \| '_ \ / _ \ |_ \| '_ \| | | |
@@ -271,10 +272,10 @@ Having `phono3py_params.yaml`, phono3py is executed with `--pypolymlp` option,
  |_|                                |_|    |___/
                                       3.11.2
 
--------------------------[time 2025-01-15 16:43:57]-------------------------
+-------------------------[time 2025-01-15 19:30:47]-------------------------
 Compiled with OpenMP support (max 10 threads).
 Running in phono3py.load mode.
-Python version 3.12.6
+Python version 3.12.3
 Spglib version 2.5.0
 ----------------------------- General settings -----------------------------
 HDF5 data compression filter: gzip
@@ -315,6 +316,7 @@ Generate random displacements
   Displacement distance: 0.001
 Evaluate forces in 400 supercells by pypolymlp
 ----------------------------- Force constants ------------------------------
+Symfc will be used to handle general (or random) displacements.
 -------------------------------- Symfc start -------------------------------
 Symfc is a force constants calculator. See the following paper:
 A. Seko and A. Togo, Phys. Rev. B, 110, 214302 (2024).
@@ -336,7 +338,7 @@ fc2 was written into "fc2.hdf5".
 ----------- None of ph-ph interaction calculation was performed. -----------
 Dataset generated using MLPs was written in "phono3py_mlp_eval_dataset.yaml".
 Summary of calculation was written in "phono3py.yaml".
--------------------------[time 2025-01-15 16:45:15]-------------------------
+-------------------------[time 2025-01-15 19:32:04]-------------------------
                  _
    ___ _ __   __| |
   / _ \ '_ \ / _` |
@@ -360,17 +362,16 @@ resulting forces are computed accordingly. The displacement distance is set by
 the `--amplitude` option, whose default value is 0.001 Angstrom. When the `--rd`
 option is used, it specifies the number of supercells with random directional
 displacements. Note that to achieve accurate force constants, the actual number
-of generated supercells is twice the specified number. Additionally, when using
-`--rd`, the `--symfc` option must be used together. If `--rd` is omitted,
-systematic displacements are introduced, and thus `--symfc` is not required.
+of generated supercells is twice the specified number. If `--rd` is omitted,
+systematic displacements are introduced.
 
 Once the file `phono3py.pmlp` is obtained, force constants can be calculated
 using MLPs from `phono3py.pmlp`. After removing the `fc3.hdf5` and `fc2.hdf5`
 files, `phono3py-load` will detect `phono3py.pmlp` and then compute the force
 constants by loading the MLPs from `phono3py.pmlp` as follows:
 
 ```
-% phono3py-load --pypolymlp --rd 100 --symfc --amplitude 0.01 phono3py.yaml
+% phono3py-load --pypolymlp --rd 100 --amplitude 0.01 phono3py.yaml
         _                      _____
   _ __ | |__   ___  _ __   ___|___ / _ __  _   _
  | '_ \| '_ \ / _ \| '_ \ / _ \ |_ \| '_ \| | | |
@@ -379,7 +380,7 @@ constants by loading the MLPs from `phono3py.pmlp` as follows:
  |_|                                |_|    |___/
                                       3.11.2
 
--------------------------[time 2025-01-12 10:08:31]-------------------------
+-------------------------[time 2025-01-15 19:28:22]-------------------------
 Compiled with OpenMP support (max 10 threads).
 Running in phono3py.load mode.
 Python version 3.12.3
@@ -395,7 +396,6 @@ Primitive matrix:
 Spacegroup: Fm-3m (225)
 Use -v option to watch primitive cell, unit cell, and supercell structures.
 NAC parameters were read from "phono3py.yaml".
------------------------------ Force constants ------------------------------
 ----------------------------- pypolymlp start ------------------------------
 Pypolymlp is a generator of polynomial machine learning potentials.
 Please cite the paper: A. Seko, J. Appl. Phys. 133, 011101 (2023).
@@ -406,6 +406,8 @@ Generate random displacements
   Twice of number of snapshots will be generated for plus-minus displacements.
   Displacement distance: 0.01
 Evaluate forces in 200 supercells by pypolymlp
+----------------------------- Force constants ------------------------------
+Symfc will be used to handle general (or random) displacements.
 -------------------------------- Symfc start -------------------------------
 Symfc is a force constants calculator. See the following paper:
 A. Seko and A. Togo, Phys. Rev. B, 110, 214302 (2024).
@@ -427,7 +429,7 @@ fc2 was written into "fc2.hdf5".
 ----------- None of ph-ph interaction calculation was performed. -----------
 Dataset generated using MLPs was written in "phono3py_mlp_eval_dataset.yaml".
 Summary of calculation was written in "phono3py.yaml".
--------------------------[time 2025-01-12 10:08:40]-------------------------
+-------------------------[time 2025-01-15 19:28:30]-------------------------
                  _
    ___ _ __   __| |
   / _ \ '_ \ / _` |