[SyneRBI/SIRF] Implement adding Hessian diagonal in SIRF (PR #1370)

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Evgueni Ovtchinnikov

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Jan 28, 2026, 10:13:38 AMJan 28
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Changes in this pull request

Testing performed

Related issues

Fixes #1369

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  • I have performed a self-review of my code
  • I have added docstrings/doxygen in line with the guidance in the developer guide
  • I have implemented unit tests that cover any new or modified functionality
  • The code builds and runs on my machine
  • CHANGES.md has been updated with any functionality change

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  • The content of this Pull Request (the Contribution) is intentionally submitted for inclusion in SIRF (the Work) under the terms and conditions of the Apache-2.0 License.

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  https://github.com/SyneRBI/SIRF/pull/1370

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Evgueni Ovtchinnikov

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Jan 28, 2026, 12:32:05 PMJan 28
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@evgueni-ovtchinnikov pushed 1 commit.

  • ae578b8 added constructor for xSTIR RDP from Gibbs RDP


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Kris Thielemans

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Jan 29, 2026, 8:12:05 AMJan 29
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KrisThielemans left a comment (SyneRBI/SIRF#1370)

I think the best strategy is to just use GibbsRelativeDifferencePenalty everywhere. It should be backwards compatible with RelativeDifferencePrior. @ColomboMatte0 is that correct? (we don't need the surrogate stuff here AFAIK)


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Matteo Colombo

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Jan 29, 2026, 11:36:51 AMJan 29
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ColomboMatte0 left a comment (SyneRBI/SIRF#1370)

It is backwards compatible with all the methods implemented in RelativedifferencePrior , we do not have SPS stuff for the RDP.


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Evgueni Ovtchinnikov

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Feb 2, 2026, 9:01:14 AMFeb 2
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@evgueni-ovtchinnikov pushed 1 commit.

  • c9ee3cc trying Kris' suggestion to derive SIRF RDP from STIR Gibbs penalty


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Evgueni Ovtchinnikov

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Feb 3, 2026, 8:58:53 AMFeb 3
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@evgueni-ovtchinnikov pushed 1 commit.

  • b67e1b0 replaced STIR RDP with SIRF RDP derived from Gibbs penalty


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Evgueni Ovtchinnikov

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Feb 5, 2026, 2:07:43 PMFeb 5
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@evgueni-ovtchinnikov pushed 1 commit.

  • 77754b4 added method compute_Hessian_gradient to SIRF RelativeDifferencePrior


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Kris Thielemans

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Feb 12, 2026, 5:31:53 AM (10 days ago) Feb 12
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KrisThielemans left a comment (SyneRBI/SIRF#1370)

@ColomboMatte0 can you suggest a test for this functionality?


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Evgueni Ovtchinnikov

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Feb 12, 2026, 7:32:15 AM (10 days ago) Feb 12
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@evgueni-ovtchinnikov pushed 1 commit.

  • bcb5a6e removed some commented-out lines [ci skip]


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Evgueni Ovtchinnikov

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Feb 16, 2026, 12:37:38 PM (6 days ago) Feb 16
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evgueni-ovtchinnikov left a comment (SyneRBI/SIRF#1370)

@ColomboMatte0 could you please suggest a Python test for this functionality. Thank you, E.


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Matteo Colombo

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Feb 16, 2026, 4:13:03 PM (6 days ago) Feb 16
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ColomboMatte0 left a comment (SyneRBI/SIRF#1370)

sorry i lost the previous notification, you mean a test for the hessian diagonal? not really sure what you mean with hessian gradient


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Kris Thielemans

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Feb 16, 2026, 4:51:35 PM (6 days ago) Feb 16
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KrisThielemans left a comment (SyneRBI/SIRF#1370)

Yes. For the diagonal (not the gradient). Not sure if we have one in STIR that could be replicated?


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Matteo Colombo

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Feb 16, 2026, 5:27:04 PM (6 days ago) Feb 16
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ColomboMatte0 left a comment (SyneRBI/SIRF#1370)

i remember i tested it numerically using finite differences from the gradient but probably those tests were not added in my PR, i can add it tomorrow, shouldn't be a big deal.


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Matteo Colombo

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Feb 16, 2026, 5:35:39 PM (6 days ago) Feb 16
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ColomboMatte0 left a comment (SyneRBI/SIRF#1370)

$$ H_{ii} \approx \frac{\nabla_i f(x + \epsilon e_i) - \nabla_i f(x - \epsilon e_i)}{2\epsilon} $$

you can test the correctness by computing this, let me know if you want me to implement it somewhere.


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Kris Thielemans

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Feb 17, 2026, 2:26:25 AM (5 days ago) Feb 17
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KrisThielemans left a comment (SyneRBI/SIRF#1370)

Good idea. I suggest to use

$$ H_{ii} \approx \frac{\nabla_i f(x + \epsilon e_i) - \nabla_i f(x)}{\epsilon} $$

a bit easier to implement, and also avoids potential issues with the RDP which is only defined on non-negative images.


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