Fix: Panel Update Bug In Fitgrains | HEXRD Discussion

Hey everyone,

We've got an interesting bug to discuss today that was found in the fitgrains section of HEXRD, specifically affecting how panels are updated. This might sound a bit technical, but stick with me, and we'll break it down. This article dives deep into the recent bug discovered in HEXRD's fitgrains.fit_grain_FF_reduced function, offering a comprehensive look at its impact, cause, and the solution implemented.

Understanding the Bug: Panel Update Issue in fitgrains

The main issue revolves around the panel variable within the fitgrains.fit_grain_FF_reduced function. The bug surfaces during the refit detector loop, where the code accesses panel pixel sizes. It turns out that the panel variable wasn't correctly set from the current det_key variable. Instead, it was holding onto the panel information from the last panel used in the detector loop, specifically from when angular tolerances were being calculated. This mix-up meant the pixel sizes being used might not match the actual panel being processed.

The problem lies in how the panel variable is handled within the fitgrains.fit_grain_FF_reduced function, particularly in the refit detector loop. The core issue is that the panel variable isn't being updated with the correct panel information for each detector. Instead, it retains the information from the last panel processed in the detector loop (used for angular tolerances). This leads to incorrect pixel sizes being accessed when dealing with multiple panels of varying types.

The Discovery and a Helpful Function

This bug was discovered while developing a new function, determine_valid_reflections(). This function streamlines the process of taking the results from pull_spots() and figuring out which spots are good (culled_results) and how complete the data is. While integrating this new function, an error popped up indicating the panel variable was undefined. This pointed to the underlying issue of the panel not being correctly updated.

The person who found this bug actually created a helpful new function called determine_valid_reflections(). This function takes the results from pull_spots() and figures out which reflections are valid, as well as the completeness of the data. By implementing this function, the code becomes more readable and organized. It was during the integration of this function that the bug was brought to light, as an error arose indicating that the panel variable was undefined in certain scenarios.

Impact Assessment: Low but Important

So, what's the real-world impact of this bug? Well, the good news is it's considered low impact for most users. The panel information is primarily used to determine pixel sizes. In many setups, especially those using multiple panels of the same type (like Dexela detectors), all panels share the same pixel sizes. This means the bug would likely go unnoticed. However, if you're working with a setup that includes different types of panels with varying pixel sizes, you might run into trouble.

While the impact of this bug is relatively low, it's crucial to address it to prevent future problems. The issue primarily affects users working with setups that include multiple panels of different kinds, as the panel pixel sizes might not be correctly accessed. This could lead to inaccuracies in data processing and analysis, highlighting the importance of the fix.

Diving Deeper: The Technical Details

Let's get a bit more technical and explore the code snippet where the bug resides. The bug occurs within the fitgrains.fit_grain_FF_reduced function, specifically in the refit detector loop. Here's a simplified view of the relevant code section:

for det_key in dets:
    # Incorrect panel access
    panel = previous_panel  # Bug: panel is not updated with det_key
    pixel_size = panel.pixel_size
    ...

In this snippet, the panel variable should be updated with the current det_key to ensure the correct panel information is used. However, the code incorrectly uses the previous_panel value, leading to the bug. This means that the pixel size being accessed belongs to the previously processed panel, causing issues when dealing with different panel types.

Reproducing the Bug

Unfortunately, there's no simple way to reproduce this bug in isolation. It manifests under specific conditions, primarily when dealing with multiple panels of different types. This makes it challenging to create a straightforward reproduction case. However, the detailed description of the bug and its location within the code provide sufficient information for developers to understand and address the issue.

Since the bug only surfaces when using multiple panels with varying pixel sizes, it's not easily reproducible in a typical setup. However, understanding the conditions under which the bug occurs helps in testing the fix and ensuring it resolves the issue effectively. The lack of a straightforward reproduction method underscores the importance of thorough code reviews and testing in complex scientific software like HEXRD.

The Fix: Ensuring Correct Panel Updates

The solution to this bug is straightforward: we need to make sure the panel variable is correctly updated within the refit detector loop. This involves assigning the correct panel corresponding to the current det_key variable.

The fix involves ensuring that the panel variable is correctly updated within the refit detector loop. This can be achieved by assigning the panel corresponding to the current det_key variable. The corrected code snippet would look like this:

for det_key in dets:
    # Correct panel access
    panel = dets[det_key]  # Fix: panel is updated with det_key
    pixel_size = panel.pixel_size
    ...

By updating the panel variable with the correct panel information for each detector, the bug is resolved. This ensures that the pixel sizes being accessed are accurate, preventing potential issues in data processing and analysis.

Pull Request Pending

To address this bug, a pull request has been submitted with the necessary changes. This pull request includes the fix described above, ensuring that the panel variable is correctly updated in the fitgrains.fit_grain_FF_reduced function. Once the pull request is reviewed and merged, the bug will be officially resolved in the next release of HEXRD.

A pull request (PR) is currently pending to incorporate this fix into the main codebase. The PR includes the corrected code snippet, ensuring that the panel variable is updated correctly within the loop. Once the PR is reviewed, approved, and merged, the fix will be part of the next HEXRD release, resolving the issue for all users.

Impact on Workflows

This bug primarily affects the HEDM (High-Energy Diffraction Microscopy) workflow. Other workflows, such as core, EDD, Powder, and Laue, are not directly affected by this issue.

The primary workflow affected by this bug is HEDM (High-Energy Diffraction Microscopy). Other workflows within HEXRD, such as core, EDD, Powder, and Laue, are not directly impacted by this issue. This targeted impact helps prioritize testing and ensures that the fix is effective for the specific workflow where the bug was identified.

Version Information

The bug was identified in the most recent version of the code at the time of discovery, specifically commit 8871889e699c23f7fb7ea6b259101c31811723f5 on the HEXRD GitHub repository.

The version of the code affected by this bug is the most recent one at the time of its discovery, which corresponds to commit 8871889e699c23f7fb7ea6b259101c31811723f5 on the HEXRD GitHub repository. This information is crucial for users who want to verify if they are affected by the bug and for developers working on the fix.

In Conclusion: A Small Bug with a Big Lesson

While this bug might seem small, it highlights the importance of careful variable handling and thorough testing, especially when dealing with complex scientific software. By identifying and addressing this issue, we're making HEXRD more robust and reliable for everyone.

This seemingly minor bug serves as a valuable lesson in the importance of meticulous variable management and comprehensive testing, especially in intricate scientific software like HEXRD. By promptly identifying and addressing this issue, the HEXRD team is enhancing the software's robustness and reliability for all users. This proactive approach ensures that potential issues are resolved before they can significantly impact research outcomes.

Thanks for tuning in, guys! We'll keep you updated on the pull request and any other developments. If you have any questions, feel free to drop them in the comments below!