Gradients example doesn't make progress on the GPU runners

[bettinaheim]

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Describe the bug

Enabling a basic validation that runs all examples on the GPU backends, the gradients example fails to make progress. Locally, everything works fine, but on the runners the values are odd:
Locally:

Optimize with no gradients.
<H>(0.000000, 0.000000) = -0.436286
<H>(1.570796, 0.000000) = 12.250291
<H>(0.000000, 1.570796) = 9.407001
<H>(-1.241051, -0.962909) = 8.691541
<H>(-0.620525, -0.481455) = 6.446059
...

On the GH runner:

Optimize with no gradients.
<H>(0.000000, 0.000000) = 15.532000
<H>(1.570796, 0.000000) = 15.532000
<H>(0.000000, 1.570796) = 15.532000
<H>(0.107242, 0.000000) = 15.532000
<H>(0.000000, 0.082867) = 15.532000
...
<H>(0.000000, 0.000000) = 15.532000
<H>(0.000000, 0.000000) = 15.532000 (keeps being this)

I haven't had a chance to look further.

May be related:
#583
#623
#399

Steps to reproduce the bug

In .github/workflows/publishing.yml enable the /home/cudaq/examples/cpp/other/gradients.cpp example in the validation job, then manually run the workflow for a recent deployment. It would be good to find a local repro, but I don't have one right now.

Expected behavior

The example should succeed.

Is this a regression? If it is, put the last known working version (or commit) here.

Not a regression

Environment

• CUDA Quantum version: latest main
• Python version: N/A
• C++ compiler: any
• Operating system: N/A

Suggestions

No response

[zaikunzhang]

Hi, I guess the optimization is done by Powell's COBYLA here. If yes, this is a known issue of the old version of COBYLA based on the original Fortran 77 implementation, which may get stuck in infinite loops. It is advised to switch to the PRIMA implementation of COBYLA. See #399 (comment). Thanks.

[schweitzpgi]

Claims to be fixed.

[1tnguyen]

Gradients example has been readded to the GPU validation test suite. Closing.