fix: allow fast_class and tcut to work together

[krystophny]

User description

Summary

• Remove incorrect validation that prevented using fast_class with positive tcut
• Fix examples/classification/simple.in to use correct VMEC file matching Makefile
• Add classifier_combined golden record test validating both classification methods work together

Root Cause

The error check added in commit d607ec1 ("feat: refresh python API classification #184") was incorrect:

if (fast_class .and. tcut > 0.0d0) then
  error stop 'fast_class and positive tcut are mutually exclusive'
endif

These are actually complementary classification methods:

• fast_class=.True. enables J_parallel and ideal orbit classifiers (runs at banana tips)
• tcut > 0 enables fractal dimension classification (runs at specified time cut)

The original working example at commit 3a771f2 used both together.

Test Plan

• make test passes (100% of 23 tests)
• Classification example examples/classification/ runs successfully
• New golden record test classifier_combined validates both methods work together
• Codex agent review approved

Related

Fixes regression where classification example would error stop with "fast_class and positive tcut are mutually exclusive"

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PR Type

Bug fix, Tests

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Description

• Remove incorrect validation preventing fast_class and tcut from working together

• These are complementary classification methods, not mutually exclusive

• Fix example configuration to use correct VMEC file matching Makefile

• Add classifier_combined golden record test validating both methods work together

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Diagram Walkthrough

flowchart LR
  A["Remove incorrect validation"] --> B["fast_class and tcut now compatible"]
  C["Fix example VMEC file reference"] --> D["QA to QH file"]
  E["Add classifier_combined test"] --> F["Validate both methods work"]
  B --> G["Classification methods work together"]
  D --> G
  F --> G

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File Walkthrough

	Relevant files
Bug fix	params.f90 Remove mutually exclusive validation for fast_class and tcut src/params.f90 Removed incorrect error check that prevented using fast_class with positive tcut These are complementary classification methods: fast_class enables J_parallel and ideal orbit classifiers, while tcut enables fractal dimension classification Validation now only checks for incompatibility with collisions +0/-3      simple.in Fix VMEC file reference in classification example                examples/classification/simple.in Changed VMEC file from wout_LandremanPaul2021_QA_reactorScale_lowres_reference.nc to wout_LandremanPaul2021_QH_reactorScale_lowres_reference.nc Corrects file reference to match the Makefile configuration +1/-1
Tests	simple.in Add classifier_combined golden record test configuration  test/golden_record/classifier_combined/simple.in New test configuration file for classifier_combined golden record test Validates that both fast_class=.True. and tcut=1d-2 work together Uses 32 test particles with deterministic mode for reproducible results Includes classification plot output configuration +15/-0

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[qodo-code-review]

PR Compliance Guide 🔍

Below is a summary of compliance checks for this PR:

Security Compliance
🟢	No security concerns identified No security vulnerabilities detected by AI analysis. Human verification advised for critical code.
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⚪	🎫 No ticket provided Create ticket/issue
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Custom Compliance
🟢	Generic: Meaningful Naming and Self-Documenting Code Objective: Ensure all identifiers clearly express their purpose and intent, making code self-documenting Status: Passed Learn more about managing compliance generic rules or creating your own custom rules
	Generic: Secure Error Handling Objective: To prevent the leakage of sensitive system information through error messages while providing sufficient detail for internal debugging. Status: Passed Learn more about managing compliance generic rules or creating your own custom rules
⚪	Generic: Comprehensive Audit Trails Objective: To create a detailed and reliable record of critical system actions for security analysis and compliance. Status: No audit logs: The change alters validation behavior for classification without introducing any logging of critical actions or outcomes, making it unclear if such actions are audited. Referred Code if (swcoll .and. (tcut > 0.0d0 .or. class_plot .or. fast_class)) then error stop 'Collisions are incompatible with classification' endif Learn more about managing compliance generic rules or creating your own custom rules
	Generic: Robust Error Handling and Edge Case Management Objective: Ensure comprehensive error handling that provides meaningful context and graceful degradation Status: Rigid error stop: The code uses a hard error stop for collision/classification incompatibility without context (e.g., parameter values), which may hinder diagnostics and graceful handling. Referred Code if (swcoll .and. (tcut > 0.0d0 .or. class_plot .or. fast_class)) then error stop 'Collisions are incompatible with classification' endif Learn more about managing compliance generic rules or creating your own custom rules
	Generic: Secure Logging Practices Objective: To ensure logs are useful for debugging and auditing without exposing sensitive information like PII, PHI, or cardholder data. Status: No structured logs: No logging was added around classification configuration decisions, offering no structured telemetry and making it unclear whether sensitive data could be inadvertently logged elsewhere. Referred Code call reset_seed_if_deterministic if (swcoll .and. (tcut > 0.0d0 .or. class_plot .or. fast_class)) then error stop 'Collisions are incompatible with classification' endif end subroutine read_config Learn more about managing compliance generic rules or creating your own custom rules
	Generic: Security-First Input Validation and Data Handling Objective: Ensure all data inputs are validated, sanitized, and handled securely to prevent vulnerabilities Status: External file input: The configuration introduces or modifies external file references (VMEC netCDF) without visible validation or sanitization in the shown diff to ensure safe handling. Referred Code netcdffile = 'wout_LandremanPaul2021_QH_reactorScale_lowres_reference.nc' ! name of VMEC file in NETCDF format isw_field_type = 2 ! -1: Testing, 0: Canonical, 1: VMEC, 2: Boozer Learn more about managing compliance generic rules or creating your own custom rules

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[qodo-code-review]

PR Code Suggestions ✨

Explore these optional code suggestions:

Category	Suggestion	Impact
General	Improve comment for clarity Improve the comment for the fast_class parameter in test/golden_record/classifier_combined/simple.in to be more descriptive and consistent with other files. test/golden_record/classifier_combined/simple.in [13] -fast_class = .True. ! if .True. quit immediately after fast classification +fast_class = .True. ! if .True. quit immediately after fast classification and don't trace orbits to the end Apply / Chat Suggestion importance[1-10]: 3 __ Why: The suggestion correctly points out an inconsistent and less descriptive comment for the fast_class parameter, and improving it enhances clarity and consistency across configuration files.	Low
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