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//! Implementation of ?gels - Solve the least squares problem A * X = B or A^H * X = B.
use std::ffi::c_char;
use lapack::{cgels, sgels, zgels};
use crate::base_types::LapackResult;
use crate::base_types::{LapackError, c32, c64};
use crate::dense::linalg::lapack::interface::lapack_return;
use num::{Zero, complex::ComplexFloat};
/// Transposition modes for `?gels`.
pub enum GelsTransMode {
/// No transpose
NoTranspose,
/// Conjugate transpose
ConjugateTranspose,
}
/// ?gels - Solve the least squares problem A * X = B or A^H * X = B.
pub trait Gels: Sized {
/// Solve the least squares problem A * X = B or A^H * X = B.
///
/// **Arguments:**
/// - `trans`: Transpose mode, either 'N' for no transpose or 'C' for conjugate transpose.
/// - `m`: Number of rows in matrix A.
/// - `n`: Number of columns in matrix A.
/// - `nrhs`: Number of right-hand sides (columns in B).
/// - `a`: The matrix A.
/// - `lda`: Leading dimension of A.
/// - `b`: The right-hand side matrix B.
/// - `ldb`: Leading dimension of B.
///
/// **Returns:**
/// A `LapackResult<()>` indicating success or failure.
#[allow(clippy::too_many_arguments)]
fn gels(
trans: GelsTransMode,
m: usize,
n: usize,
nrhs: usize,
a: &mut [Self],
lda: usize,
b: &mut [Self],
ldb: usize,
) -> LapackResult<()>;
}
trait TransposeToChar {
fn to_char(trans: GelsTransMode) -> u8;
}
macro_rules! implement_transpose_to_char {
($scalar:ty, $char:expr) => {
impl TransposeToChar for $scalar {
fn to_char(trans: GelsTransMode) -> u8 {
match trans {
GelsTransMode::NoTranspose => b'N',
GelsTransMode::ConjugateTranspose => $char,
}
}
}
};
}
implement_transpose_to_char!(f32, b'T');
implement_transpose_to_char!(f64, b'T');
implement_transpose_to_char!(c32, b'C');
implement_transpose_to_char!(c64, b'C');
macro_rules! implement_gels {
($scalar:ty, $gels:expr) => {
impl Gels for $scalar {
fn gels(
trans: GelsTransMode,
m: usize,
n: usize,
nrhs: usize,
a: &mut [Self],
lda: usize,
b: &mut [Self],
ldb: usize,
) -> LapackResult<()> {
let mut info = 0;
assert_eq!(
a.len(),
lda * n,
"Require `a.len()` {} == `lda * n` {}.",
a.len(),
lda * n
);
assert!(
lda >= std::cmp::max(1, m),
"Require `lda` {} >= `max(1, m)` {}.",
lda,
std::cmp::max(1, m)
);
assert_eq!(
b.len(),
ldb * nrhs,
"Require `b.len()` {} == `ldb * nrhs` {}.",
b.len(),
ldb * nrhs
);
assert!(
ldb >= std::cmp::max(1, std::cmp::max(m, n)),
"Require `ldb` {} >= `max(1, max(m, n))` {}.",
ldb,
std::cmp::max(1, std::cmp::max(m, n))
);
let mut work = vec![<$scalar>::zero(); 1];
let trans = <$scalar as TransposeToChar>::to_char(trans);
unsafe {
$gels(
trans,
m as i32,
n as i32,
nrhs as i32,
a,
lda as i32,
b,
ldb as i32,
&mut work,
-1,
&mut info,
);
}
if info != 0 {
return Err(LapackError::LapackInfoCode(info));
}
let lwork = work[0].re() as i32;
let mut work = vec![<$scalar>::zero(); lwork as usize];
unsafe {
$gels(
trans,
m as i32,
n as i32,
nrhs as i32,
a,
lda as i32,
b,
ldb as i32,
&mut work,
lwork,
&mut info,
);
}
lapack_return(info, ())
}
}
};
}
unsafe extern "C" {
/// FFI bindings for the LAPACK `dgels` function.
///
/// This is necessary because of a bug in the `lapack-sys` library that adds a non-existent
/// parameter to the `dgels` signature.
pub fn dgels_(
trans: *const std::ffi::c_char,
m: *const std::ffi::c_int,
n: *const std::ffi::c_int,
nrhs: *const std::ffi::c_int,
A: *mut f64,
lda: *const std::ffi::c_int,
B: *mut f64,
ldb: *const std::ffi::c_int,
work: *mut f64,
lwork: *const std::ffi::c_int,
info: *mut std::ffi::c_int,
);
}
#[inline]
#[allow(clippy::too_many_arguments)]
unsafe fn dgels(
trans: u8,
m: i32,
n: i32,
nrhs: i32,
a: &mut [f64],
lda: i32,
b: &mut [f64],
ldb: i32,
work: &mut [f64],
lwork: i32,
info: &mut i32,
) {
unsafe {
dgels_(
&(trans as c_char),
&m,
&n,
&nrhs,
a.as_mut_ptr(),
&lda,
b.as_mut_ptr(),
&ldb,
work.as_mut_ptr(),
&lwork,
info,
)
}
}
implement_gels!(f32, sgels);
implement_gels!(f64, dgels);
implement_gels!(c32, cgels);
implement_gels!(c64, zgels);