Cannot Repeat HHL Example Result

[hywong2]

Informations

• Qiskit version: 0.25.0
• Python version: 3.8
• Operating system: CentOS 7

What is the current behavior?

There is an HHL example in IBM Qiskit

https://qiskit.org/textbook/ch-applications/hhl_tutorial.html

If I run on that website (click "Try") in Section 4 and set time=np.pi*3/4, I get 100% fidelity as expected. However, if I copy those code and run it on my server or in the IBM Q account, it is no longer 100%.

I also try with my other matrix which I expect to have an exact solution. Again, I get 100% fidelity if I modify the code in that website but I get only 80% if I run on my server. The matrix I am trying is [[1 -0.5],[-0.5, 1]] which has an exact solution if time=np.pi.

Steps to reproduce the problem

What is the expected behavior?

Suggested solutions

If I use python 3.7.3 (3.8 won't work) + qiskit 0.23.5, I can get fidelity = 1.