Document project-specific dependency constraints and DAE scipy requirement

- Add documentation on when and why to use tighter constraints
- Document DAE project's scipy<1.15 requirement
- Add explanatory comment in DAE environment.yml
- Provide best practices for handling project-specific needs

Co-authored-by: pancetta <[email protected]>

Author: Copilot

docs/contrib/08_dependency_management.md

@@ -272,6 +272,29 @@ When creating a new project in `pySDC/projects/`:
 
 See [Adding a Project](./06_new_project.md) for more details.
 
+### Project-Specific Constraints
+
+Some projects have **tighter version constraints** than the general guidelines due to specific requirements:
+
+**Example: DAE Project**
+```yaml
+dependencies:
+  - scipy>=0.17.1,<1.15  # Tighter than general <2.0 constraint
+```
+
+**Reason**: The DAE project contains tests for fully implicit index-2 differential-algebraic equation solvers that are sensitive to numerical precision changes. Scipy versions >= 1.15 introduce minor numerical differences that cause test failures in convergence order tests.
+
+**When to use tighter constraints**:
+- Numerical precision requirements in scientific computing
+- Known compatibility issues with specific version ranges
+- Project relies on deprecated features being removed in newer versions
+
+**Best practices**:
+- Document the reason in the project README or environment file
+- Add a comment explaining why the constraint is tighter
+- Periodically review if the constraint can be relaxed
+- Consider opening an issue to track updating code for newer versions
+
 ## Examples
 
 ### Good Dependency Specification
@@ -293,6 +316,8 @@ dependencies:
     - qmat>=0.1.8
 ```
 
+**Note**: Some projects may require tighter constraints due to numerical precision requirements. For example, the DAE project uses `scipy>=0.17.1,<1.15` because newer scipy versions introduce numerical differences that affect the fully implicit index-2 DAE solver tests. Always respect project-specific constraints when they exist.
+
 ### Version Constraint Patterns
 
 - **Stable, mature libraries**: `numpy>=1.15.4,<3.0` (allow minor updates within major version)

pySDC/projects/DAE/environment.yml

@@ -5,6 +5,8 @@ channels:
   - conda-forge
 dependencies:
   - numpy>=1.15.4,<3.0
+  # scipy<1.15 required: newer versions cause numerical precision differences
+  # in fully implicit index-2 DAE solver tests (convergence order tests)
   - scipy>=0.17.1,<1.15
   - dill>=0.2.6
   - mpich