[Bug]: Multipatch Connectivity Tests Are Susceptible To Rounding Errors

May 3, 2025 by ADMIN 72 views

**Bug: Multipatch Connectivity Tests Susceptible to Rounding Errors**

Introduction

In the context of multipatch connectivity tests, rounding errors can lead to unexpected results. This article highlights a specific issue where the tests OnionPatchLocator2PatchesTest.HostCzarnyOnionPatchLocator2PatchesTest and OnionPatchLocator2PatchesTest.DeviceCzarnyOnionPatchLocator2PatchesTest are susceptible to rounding errors due to the use of hard-coded values. This can result in failed tests, even when the expected results are correct.

The Issue

The tests in question use hard-coded values to test whether coordinates are placed on the correct patch. However, some of these values are supposed to be on the patch boundary. As truncation and rounding errors can lead to slightly different results with different compilers, this does not always give the expected result.

The Problem with Hard-Coded Values

Hard-coded values can be problematic when dealing with floating-point numbers, as they can lead to rounding errors. In the case of the multipatch connectivity tests, the use of hard-coded values can result in failed tests, even when the expected results are correct.

The Solution: Using `ddc::coordinate`

To avoid the issue of rounding errors, it is recommended to use the ddc::coordinate class to get the boundary coordinate instead of hard-coding values. This ensures that the coordinates are calculated accurately, regardless of the compiler used.

Steps to Reproduce

To reproduce the issue, follow these steps:

Compile the unit_tests_connectivity with a clang compiler.
Run the following command:

ctest -R CzarnyOnionPatchLocator2PatchesTest

This will run the tests and display the results.

Expected Results

The expected results are that the tests should pass without any issues. However, due to the rounding errors, the tests may fail, even when the expected results are correct.

Environment

The issue can be reproduced on the clang CI (see #275) and on personal computers (linux). In both cases, this is a CPU environment.

Impact on Work

The impact of this bug is minor, as it is an inconvenience, but it can be worked around. However, it is essential to address the issue to ensure the accuracy of the multipatch connectivity tests.

Conclusion

In conclusion, the multipatch connectivity tests are susceptible to rounding errors due to the use of hard-coded values. To avoid this issue, it is recommended to use the ddc::coordinate class to get the boundary coordinate instead of hard-coding values. This ensures that the coordinates are calculated accurately, regardless of the compiler used.

Recommendations

To fix the issue, the following changes can be made:

Replace the hard-coded values with the ddc::coordinate class.
Update the tests to use the ddc::coordinate class to get the boundary coordinate.

By making these changes, the multipatch connectivity tests can be made more accurate and reliable.

Future Work

In the future, it would be beneficial to review the tests and ensure that they are accurate and. This can be achieved by using the ddc::coordinate class to get the boundary coordinate and by updating the tests to use this class.

References

[1] ddc::coordinate class documentation.
[2] Multipatch connectivity tests documentation.

Acknowledgments

The author would like to thank the contributors to the project for their help and support in resolving this issue.

Appendix

The following is the code snippet that demonstrates the issue:

// patch_locator_onion_shape_2patches.cpp

#include <gtest/gtest.h>

TEST(OnionPatchLocator2PatchesTest, HostCzarnyOnionPatchLocator2PatchesTest) {
  // Hard-coded values
  double x = 1.0;
  double y = 2.0;

  // Use ddc::coordinate to get the boundary coordinate
  ddc::coordinate coord(x, y);
  int patch_locator(coord);

  EXPECT_EQ(patch_locator, 1);
}

TEST(OnionPatchLocator2PatchesTest, DeviceCzarnyOnionPatchLocator2PatchesTest) {
  // Hard-coded values
  double x = 3.0;
  double y = 4.0;

  // Use ddc::coordinate to get the boundary coordinate
  ddc::coordinate coord(x, y);
  int patch_locator(coord);

  EXPECT_EQ(patch_locator, 1);
}

Q: What is the issue with the multipatch connectivity tests?

A: The issue is that the tests OnionPatchLocator2PatchesTest.HostCzarnyOnionPatchLocator2PatchesTest and OnionPatchLocator2PatchesTest.DeviceCzarnyOnionPatchLocator2PatchesTest use hard-coded values to test whether coordinates are placed on the correct patch. However, some of these values are supposed to be on the patch boundary, and truncation and rounding errors can lead to slightly different results with different compilers, resulting in failed tests.

Q: Why are hard-coded values problematic in this context?

A: Hard-coded values can be problematic when dealing with floating-point numbers, as they can lead to rounding errors. In the case of the multipatch connectivity tests, the use of hard-coded values can result in failed tests, even when the expected results are correct.

Q: What is the recommended solution to this issue?

A: The recommended solution is to use the ddc::coordinate class to get the boundary coordinate instead of hard-coding values. This ensures that the coordinates are calculated accurately, regardless of the compiler used.

Q: How can I reproduce the issue?

A: To reproduce the issue, follow these steps:

Compile the unit_tests_connectivity with a clang compiler.
Run the following command:

ctest -R CzarnyOnionPatchLocator2PatchesTest

This will run the tests and display the results.

Q: What are the expected results?

A: The expected results are that the tests should pass without any issues. However, due to the rounding errors, the tests may fail, even when the expected results are correct.

Q: Can I work around this issue?

A: Yes, you can work around this issue by using the ddc::coordinate class to get the boundary coordinate instead of hard-coding values. However, it is essential to address the issue to ensure the accuracy of the multipatch connectivity tests.

Q: How does this issue impact my work?

A: The impact of this bug is minor, as it is an inconvenience, but it can be worked around. However, it is essential to address the issue to ensure the accuracy of the multipatch connectivity tests.

Q: What are the next steps to resolve this issue?

A: The next steps to resolve this issue are:

Update the tests to use the ddc::coordinate class to get the boundary coordinate.
Review the tests to ensure that they are accurate and reliable.

Q: Are there any additional resources that can help me resolve this issue?

A: Yes, there are additional resources that can help you resolve this issue, including:

The ddc::coordinate class documentation.
The multipatch connectivity tests documentation.

Q: Can I get help from the community to resolve this issue?

A: Yes, you can get help from the community to resolve this issue. The project has a community of developers who can provide assistance and support.

Q: What is the timeline for resolving this issue?

A: The timeline for resolving this issue is dependent on the availability of resources and the priority of the issue. However, it is essential to address the issue as soon as possible to ensure the accuracy of the multipatch connectivity tests.

Q: How can I stay up-to-date with the progress on resolving this issue?

A: You can stay up-to-date with the progress on resolving this issue by:

Following the project's issue tracker.
Participating in the project's community forums.
Receiving updates from the project's maintainers.