2D SVD function

[LeWerner42]

Category

• New feature
• Bugfix
• Breaking change
• Refactoring
• Documentation
• Other (please explain)

Description

Closes #436. This PR introduces a simple 2D SVD function. Some simulations only require 2D considerations.
Verified with the added test.
Simple Code for external testing:

import numpy as np
import warp as wp

N_tests = 1000

A_mat = np.random.randn(N_tests, 2, 2)/1e3
B_mat = np.identity(2, dtype=np.float64)
A_mat = A_mat + 0.5* B_mat

U_np, S_np, Vt_np = np.linalg.svd(A_mat, full_matrices=False)
B_mat = U_np @ (S_np[..., None]*Vt_np)

A_wp = wp.array(A_mat, dtype=wp.mat22d, shape=N_tests)
B_wp = wp.array(A_mat, dtype=wp.mat22d, shape=N_tests)
S_wp = wp.array(np.zeros((N_tests, 2)), dtype=wp.vec2d)

@wp.kernel
def SVD_wp(A:wp.array(dtype=wp.mat22d),
           B:wp.array(dtype=wp.mat22d),
           S_out:wp.array(dtype=wp.vec2d)):
    p = wp.tid()

    U = wp.mat22d()
    S = wp.vec2d()
    V = wp.mat22d()

    wp.svd2(A[p], U, S, V)
    B[p] = U * wp.diag(S) * wp.transpose(V)
    S_out[p] = S

    
wp.launch(kernel=SVD_wp, dim=N_tests, inputs=[A_wp, B_wp, S_wp])
A_wp = A_wp.numpy()
B_wp = B_wp.numpy()
S_wp = S_wp.numpy()

# avgError
print(f"mean err: {np.mean(np.abs(A_wp - B_wp))}")
print(f"std err:  {np.std(np.abs(A_wp - B_wp))}")

Limitations

Other Matrix operations are not yet implemented for 2D (e.g. qr, eig)

Changelog

• svd.h: added 2d svd function + adj_svd2
• subs: added 2d svd
• functions.rst 2d svd description
• builtins.py: added block for svd2
• test_mat.py: test for svd2 copied from svd3 and modified accordingly

Before your PR is "Ready for review"

• Do you agree to the terms under which contributions are accepted as described in Section 9 the Warp License?
• Have you read the Contributor Guidelines?
• Have you written any new necessary tests?
• Have you added or updated any necessary documentation?
• Have you added any files modified by compiling Warp and building the documentation to this PR (.e.g. stubs.py, functions.rst)?
• Does your code pass ruff check and ruff format --check?

[mmacklin]

Very nice! Thank you, we will review and get this merged.

[LeWerner42]

I am not quite sure, what the original issue with https://github.com/NVIDIA/warp/actions/runs/12816118282/job/35759531768 was.
I re-compiled the docs following the guidelines again with the last commit. (and added the forgotten entry in the changelog)

hope, this fixes it.

[shi-eric]

Looks like this merge request went in via 336fbbe but it didn't automatically close due to differences how the merge was done. Thanks @LeWerner42 for the contribution and @gdaviet for reviewing.