Modular Procedure Programming Paradigm

The repository introduces the concept of

• Modular Procedures
• Fortran Package Manager

for the Fortran phase-field codes.

This repository advances beyond the external procedures approach by introducing two fundamental improvements that transform how phase field simulations should be developed, maintained, and executed.

Feature 1: Modules Instead of External Subprograms and Interface Blocks

The Problem with External Procedures is summarized below in the table

Aspect	External Procedures	Modules
Interface blocks	Required (explicit)	Automatic (implicitly explicit)
EXTERNAL statement	needed for subroutine	Not needed
Code duplication	High	Not needed
Maintenance	High	Very low
Type safety	Compiler-dependent	Guaranteed

The basic idea of the modular procedures is to improve the aspects of the external procedures.

The Solution to the external procedures is the Modular Architecture where INTERFACE blocks and EXTERNAL statements disappear entirely:

Feature	Traditional Repository	This repository
Code organization	External procedure + Interface blocks	modules
Interface handling	Manual interface blocks	automatic
Build system	Batch files	fpm (cross-platform)
maintenance	High	low
code duplication	High	none

Feature 2: fpm (Fortran Package Manager) as Build Tool

The Problem with Manual Building

The previous repository used Windows batch files for compilation:

gfortran main.f90 fluctuation.f90 chemical_potential.f90 laplace.f90 post_processing.f90 -o main

main

Problems with this approach:

❌ No dependency tracking

❌ Must recompile everything for any change

❌ No support for different build configurations

❌ No automatic testing

❌ Difficult to manage external dependencies

❌ Platform-specific (Windows only)

The Solution: fpm

With fpm, building becomes a single command:

fpm build          # Build the project
fpm run            # Build and run
fpm test           # Run tests
fpm run --profile release  # Optimized build

fpm project structure

The fpm project struture for our phase field codes (e.g. model A) looks like

model_A/
├── fpm.toml                # Project manifest
├── app/
│   └── main.f90            # Main program
├── src/
│   ├── chemical_potential.f90
│   ├── fluctuation.f90
│   ├── laplace.f90
|   └── post_processing.f90
├── test/
|   └── check.f90
├── parameters.txt                   ← Created at runtime
└── phi_1500.dat                     ← Created at runtime

Comparison test

To understand the difference between the two approaches i.e. external procedures with windows batch file and procedural program with fpm, run both codes with fpm. You probably catch a bug!

Migration from External Procedures

1. Replace INTERFACE blocks with MODULE containing the procedures

2. Remove EXTERNAL statements - not needed with modules

3. Add USE statements instead of interface blocks

4. Create fpm.toml manifest

5. Move files to src directories

6. Build with fpm build instead of batch files

Contact

In case, you find issues to report or having trouble using the codes, you may contact via email

shahid@njust.edu.cn

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Date : 08 June 2026