qr/
qr.rs

1//! Minimal cuSOLVER dense QR factorization demo.
2//!
3//! Factorizes a small column-major `f32` matrix into `A = Q · R` via
4//! `cusolverDnSgeqrf` and prints the upper-triangular `R` plus the
5//! Householder reflector scalars `tau`. After `geqrf` the input buffer
6//! holds `R` in the upper triangle and the implicit reflectors in the
7//! lower triangle.
8//!
9//! Run with:
10//!
11//! ```text
12//! cargo run --example qr -p baracuda-cusolver
13//! ```
14
15use baracuda_cusolver::{geqrf, DnHandle};
16use baracuda_driver::{Context, Device, DeviceBuffer};
17
18fn main() -> Result<(), Box<dyn std::error::Error>> {
19    baracuda_driver::init()?;
20    let device = Device::get(0)?;
21    println!("device: {}", device.name()?);
22    let ctx = Context::new(&device)?;
23    let handle = DnHandle::new()?;
24
25    // 3×3 column-major:
26    //   A = [[12, -51,   4],
27    //        [ 6, 167, -68],
28    //        [-4,  24, -41]]
29    // Stored as columns: [12, 6, -4,  -51, 167, 24,  4, -68, -41]
30    let m: i32 = 3;
31    let n: i32 = 3;
32    let lda: i32 = m;
33    let a_host: [f32; 9] = [12.0, 6.0, -4.0, -51.0, 167.0, 24.0, 4.0, -68.0, -41.0];
34
35    let mut a = DeviceBuffer::from_slice(&ctx, &a_host)?;
36    let mut tau: DeviceBuffer<f32> = DeviceBuffer::new(&ctx, m.min(n) as usize)?;
37    let mut info: DeviceBuffer<i32> = DeviceBuffer::new(&ctx, 1)?;
38
39    geqrf::<f32>(&handle, m, n, &mut a, lda, &mut tau, &mut info)?;
40
41    let mut info_host = [42i32];
42    info.copy_to_host(&mut info_host)?;
43    assert_eq!(info_host[0], 0, "geqrf info = {}", info_host[0]);
44
45    let mut a_out = [0.0f32; 9];
46    a.copy_to_host(&mut a_out)?;
47    let mut tau_out = vec![0.0f32; tau.len()];
48    tau.copy_to_host(&mut tau_out)?;
49
50    // Print R (the upper triangle of `a` after geqrf, column-major).
51    println!("R (upper triangle, in column-major positions):");
52    for i in 0..m as usize {
53        for j in 0..n as usize {
54            if i <= j {
55                print!("{:10.4} ", a_out[j * lda as usize + i]);
56            } else {
57                print!("{:>10} ", "·");
58            }
59        }
60        println!();
61    }
62    println!("tau = {tau_out:?}");
63
64    // For this fixture the magnitude of R[0,0] is sqrt(12^2 + 6^2 + 4^2) = 14.
65    let r00 = a_out[0].abs();
66    assert!((r00 - 14.0).abs() < 1e-3, "R[0,0]={r00}, expected 14");
67    println!("OK (|R[0,0]| = {r00})");
68    Ok(())
69}
qr/qr.rs

qr/
qr.rs
