Computation of Coverage Map with RIS module existence on GPU

[Sina7474]

Hello,

I am working with Sionna ray tracing (both versions 0.19.0 and 0.19.2), specifically using the Coverage Map function along with the RIS module. I have developed a code to compute coverage maps for specific tiles while deploying an RIS. The code runs on the GPU of a Linux machine.
However, I encountered a strange issue. When using an RIS with a large number of elements (e.g., 100×100 or even 20×20), and enabling scattering or reflection in the Coverage Map function, I get the following error:

__wrapped__Svd_device_/job:localhost/replica:0/task:0/device:GPU:0}} Got info = 2 for batch index 0, expected info = 0. Debug_info = gesvd [Op:Svd] name:

This error only occurs when running the simulation on the GPU. If I run it on the CPU, the problem does not appear. Also, if I disable reflection, the simulation works correctly, even on the GPU.

Could you please advise me on how to solve or work around this problem?

[jhoydis]

Hi @Sina7474,

Would you have a reproducer code snippet for this issue?

[Sina7474]

Hello @jhoydis

I resolved this issue by modifying the tf.linalg.svd computation in the source code. Specifically, in the solver_cm.py script, I replaced the following line:

e, v, _ = tf.linalg.svd(q_r)

with the following code:

eps = tf.cast(1e-12, q_r.dtype)
q_r_safe = tf.where(tf.math.is_finite(q_r), q_r, tf.zeros_like(q_r))
q_r_safe += eps * tf.eye(3, batch_shape=tf.shape(q_r)[:1], dtype=q_r.dtype)
e, v, _ = tf.linalg.svd(q_r_safe, full_matrices=False)

The issue arises when using RIS in Sionna: in certain cases, computing 1/curvature results in inf or nan, which causes the SVD to fail. This fix adds a small regularization term and handles non-finite values to ensure numerical stability.
Running the code on a CPU with sufficient memory (e.g., 128 GB) does not pose a problem. However, on a GPU, due to limited memory, the computation can crash after several RIS placements (as part of location optimization). This patch prevents such crashes during those iterations.

Thanks again for your response and for your efforts in addressing the issue!

Best,
Sina