719 lines
25 KiB
Rust
719 lines
25 KiB
Rust
#[cfg(feature = "serde-serialize")]
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use serde::{Deserialize, Serialize};
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use approx::AbsDiffEq;
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use num::{One, Zero};
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use crate::allocator::Allocator;
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use crate::base::{DefaultAllocator, Matrix, Matrix2x3, MatrixMN, Vector2, VectorN};
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use crate::constraint::{SameNumberOfRows, ShapeConstraint};
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use crate::dimension::{Dim, DimDiff, DimMin, DimMinimum, DimSub, U1, U2};
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use crate::storage::Storage;
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use simba::scalar::{ComplexField, RealField};
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use crate::linalg::givens::GivensRotation;
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use crate::linalg::symmetric_eigen;
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use crate::linalg::Bidiagonal;
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/// Singular Value Decomposition of a general matrix.
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#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
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#[cfg_attr(
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feature = "serde-serialize",
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serde(bound(
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serialize = "DefaultAllocator: Allocator<N::RealField, DimMinimum<R, C>> +
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Allocator<N, DimMinimum<R, C>, C> +
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Allocator<N, R, DimMinimum<R, C>>,
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MatrixMN<N, R, DimMinimum<R, C>>: Serialize,
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MatrixMN<N, DimMinimum<R, C>, C>: Serialize,
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VectorN<N::RealField, DimMinimum<R, C>>: Serialize"
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))
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)]
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#[cfg_attr(
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feature = "serde-serialize",
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serde(bound(
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deserialize = "DefaultAllocator: Allocator<N::RealField, DimMinimum<R, C>> +
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Allocator<N, DimMinimum<R, C>, C> +
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Allocator<N, R, DimMinimum<R, C>>,
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MatrixMN<N, R, DimMinimum<R, C>>: Deserialize<'de>,
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MatrixMN<N, DimMinimum<R, C>, C>: Deserialize<'de>,
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VectorN<N::RealField, DimMinimum<R, C>>: Deserialize<'de>"
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))
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)]
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#[derive(Clone, Debug)]
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pub struct SVD<N: ComplexField, R: DimMin<C>, C: Dim>
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where
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DefaultAllocator: Allocator<N, DimMinimum<R, C>, C>
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+ Allocator<N, R, DimMinimum<R, C>>
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+ Allocator<N::RealField, DimMinimum<R, C>>,
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{
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/// The left-singular vectors `U` of this SVD.
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pub u: Option<MatrixMN<N, R, DimMinimum<R, C>>>,
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/// The right-singular vectors `V^t` of this SVD.
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pub v_t: Option<MatrixMN<N, DimMinimum<R, C>, C>>,
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/// The singular values of this SVD.
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pub singular_values: VectorN<N::RealField, DimMinimum<R, C>>,
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}
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impl<N: ComplexField, R: DimMin<C>, C: Dim> Copy for SVD<N, R, C>
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where
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DefaultAllocator: Allocator<N, DimMinimum<R, C>, C>
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+ Allocator<N, R, DimMinimum<R, C>>
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+ Allocator<N::RealField, DimMinimum<R, C>>,
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MatrixMN<N, R, DimMinimum<R, C>>: Copy,
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MatrixMN<N, DimMinimum<R, C>, C>: Copy,
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VectorN<N::RealField, DimMinimum<R, C>>: Copy,
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{
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}
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impl<N: ComplexField, R: DimMin<C>, C: Dim> SVD<N, R, C>
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where
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DimMinimum<R, C>: DimSub<U1>, // for Bidiagonal.
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DefaultAllocator: Allocator<N, R, C>
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+ Allocator<N, C>
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+ Allocator<N, R>
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+ Allocator<N, DimDiff<DimMinimum<R, C>, U1>>
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+ Allocator<N, DimMinimum<R, C>, C>
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+ Allocator<N, R, DimMinimum<R, C>>
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+ Allocator<N, DimMinimum<R, C>>
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+ Allocator<N::RealField, DimMinimum<R, C>>
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+ Allocator<N::RealField, DimDiff<DimMinimum<R, C>, U1>>,
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{
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/// Computes the Singular Value Decomposition of `matrix` using implicit shift.
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pub fn new(matrix: MatrixMN<N, R, C>, compute_u: bool, compute_v: bool) -> Self {
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Self::try_new(
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matrix,
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compute_u,
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compute_v,
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N::RealField::default_epsilon(),
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0,
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)
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.unwrap()
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}
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/// Attempts to compute the Singular Value Decomposition of `matrix` using implicit shift.
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///
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/// # Arguments
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///
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/// * `compute_u` − set this to `true` to enable the computation of left-singular vectors.
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/// * `compute_v` − set this to `true` to enable the computation of left-singular vectors.
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/// * `eps` − tolerance used to determine when a value converged to 0.
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/// * `max_niter` − maximum total number of iterations performed by the algorithm. If this
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/// number of iteration is exceeded, `None` is returned. If `niter == 0`, then the algorithm
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/// continues indefinitely until convergence.
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pub fn try_new(
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mut matrix: MatrixMN<N, R, C>,
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compute_u: bool,
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compute_v: bool,
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eps: N::RealField,
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max_niter: usize,
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) -> Option<Self> {
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assert!(
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matrix.len() != 0,
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"Cannot compute the SVD of an empty matrix."
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);
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let (nrows, ncols) = matrix.data.shape();
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let min_nrows_ncols = nrows.min(ncols);
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let dim = min_nrows_ncols.value();
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let m_amax = matrix.camax();
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if !m_amax.is_zero() {
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matrix.unscale_mut(m_amax);
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}
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let b = Bidiagonal::new(matrix);
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let mut u = if compute_u { Some(b.u()) } else { None };
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let mut v_t = if compute_v { Some(b.v_t()) } else { None };
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let mut diagonal = b.diagonal();
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let mut off_diagonal = b.off_diagonal();
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let mut niter = 0;
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let (mut start, mut end) = Self::delimit_subproblem(
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&mut diagonal,
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&mut off_diagonal,
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&mut u,
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&mut v_t,
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b.is_upper_diagonal(),
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dim - 1,
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eps,
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);
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while end != start {
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let subdim = end - start + 1;
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// Solve the subproblem.
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if subdim > 2 {
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let m = end - 1;
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let n = end;
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let mut vec;
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{
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let dm = diagonal[m];
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let dn = diagonal[n];
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let fm = off_diagonal[m];
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let tmm = dm * dm + off_diagonal[m - 1] * off_diagonal[m - 1];
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let tmn = dm * fm;
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let tnn = dn * dn + fm * fm;
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let shift = symmetric_eigen::wilkinson_shift(tmm, tnn, tmn);
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vec = Vector2::new(
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diagonal[start] * diagonal[start] - shift,
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diagonal[start] * off_diagonal[start],
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);
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}
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for k in start..n {
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let m12 = if k == n - 1 {
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N::RealField::zero()
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} else {
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off_diagonal[k + 1]
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};
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let mut subm = Matrix2x3::new(
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diagonal[k],
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off_diagonal[k],
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N::RealField::zero(),
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N::RealField::zero(),
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diagonal[k + 1],
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m12,
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);
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if let Some((rot1, norm1)) = GivensRotation::cancel_y(&vec) {
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rot1.inverse()
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.rotate_rows(&mut subm.fixed_columns_mut::<U2>(0));
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let rot1 = GivensRotation::new_unchecked(rot1.c(), N::from_real(rot1.s()));
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if k > start {
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// This is not the first iteration.
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off_diagonal[k - 1] = norm1;
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}
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let v = Vector2::new(subm[(0, 0)], subm[(1, 0)]);
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// FIXME: does the case `v.y == 0` ever happen?
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let (rot2, norm2) = GivensRotation::cancel_y(&v)
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.unwrap_or((GivensRotation::identity(), subm[(0, 0)]));
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rot2.rotate(&mut subm.fixed_columns_mut::<U2>(1));
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let rot2 = GivensRotation::new_unchecked(rot2.c(), N::from_real(rot2.s()));
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subm[(0, 0)] = norm2;
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if let Some(ref mut v_t) = v_t {
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if b.is_upper_diagonal() {
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rot1.rotate(&mut v_t.fixed_rows_mut::<U2>(k));
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} else {
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rot2.rotate(&mut v_t.fixed_rows_mut::<U2>(k));
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}
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}
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if let Some(ref mut u) = u {
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if b.is_upper_diagonal() {
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rot2.inverse()
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.rotate_rows(&mut u.fixed_columns_mut::<U2>(k));
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} else {
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rot1.inverse()
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.rotate_rows(&mut u.fixed_columns_mut::<U2>(k));
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}
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}
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diagonal[k + 0] = subm[(0, 0)];
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diagonal[k + 1] = subm[(1, 1)];
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off_diagonal[k + 0] = subm[(0, 1)];
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if k != n - 1 {
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off_diagonal[k + 1] = subm[(1, 2)];
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}
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vec.x = subm[(0, 1)];
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vec.y = subm[(0, 2)];
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} else {
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break;
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}
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}
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} else if subdim == 2 {
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// Solve the remaining 2x2 subproblem.
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let (u2, s, v2) = compute_2x2_uptrig_svd(
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diagonal[start],
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off_diagonal[start],
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diagonal[start + 1],
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compute_u && b.is_upper_diagonal() || compute_v && !b.is_upper_diagonal(),
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compute_v && b.is_upper_diagonal() || compute_u && !b.is_upper_diagonal(),
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);
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let u2 = u2.map(|u2| GivensRotation::new_unchecked(u2.c(), N::from_real(u2.s())));
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let v2 = v2.map(|v2| GivensRotation::new_unchecked(v2.c(), N::from_real(v2.s())));
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diagonal[start + 0] = s[0];
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diagonal[start + 1] = s[1];
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off_diagonal[start] = N::RealField::zero();
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if let Some(ref mut u) = u {
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let rot = if b.is_upper_diagonal() {
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u2.unwrap()
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} else {
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v2.unwrap()
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};
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rot.rotate_rows(&mut u.fixed_columns_mut::<U2>(start));
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}
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if let Some(ref mut v_t) = v_t {
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let rot = if b.is_upper_diagonal() {
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v2.unwrap()
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} else {
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u2.unwrap()
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};
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rot.inverse().rotate(&mut v_t.fixed_rows_mut::<U2>(start));
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}
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end -= 1;
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}
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// Re-delimit the subproblem in case some decoupling occurred.
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let sub = Self::delimit_subproblem(
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&mut diagonal,
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&mut off_diagonal,
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&mut u,
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&mut v_t,
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b.is_upper_diagonal(),
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end,
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eps,
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);
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start = sub.0;
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end = sub.1;
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niter += 1;
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if niter == max_niter {
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return None;
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}
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}
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diagonal *= m_amax;
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// Ensure all singular value are non-negative.
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for i in 0..dim {
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let sval = diagonal[i];
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if sval < N::RealField::zero() {
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diagonal[i] = -sval;
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if let Some(ref mut u) = u {
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u.column_mut(i).neg_mut();
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}
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}
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}
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Some(Self {
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u,
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v_t,
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singular_values: diagonal,
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})
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}
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/*
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fn display_bidiag(b: &Bidiagonal<N, R, C>, begin: usize, end: usize) {
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for i in begin .. end {
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for k in begin .. i {
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print!(" ");
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}
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println!("{} {}", b.diagonal[i], b.off_diagonal[i]);
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}
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for k in begin .. end {
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print!(" ");
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}
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println!("{}", b.diagonal[end]);
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}
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*/
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fn delimit_subproblem(
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diagonal: &mut VectorN<N::RealField, DimMinimum<R, C>>,
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off_diagonal: &mut VectorN<N::RealField, DimDiff<DimMinimum<R, C>, U1>>,
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u: &mut Option<MatrixMN<N, R, DimMinimum<R, C>>>,
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v_t: &mut Option<MatrixMN<N, DimMinimum<R, C>, C>>,
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is_upper_diagonal: bool,
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end: usize,
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eps: N::RealField,
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) -> (usize, usize) {
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let mut n = end;
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while n > 0 {
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let m = n - 1;
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if off_diagonal[m].is_zero()
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|| off_diagonal[m].norm1() <= eps * (diagonal[n].norm1() + diagonal[m].norm1())
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{
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off_diagonal[m] = N::RealField::zero();
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} else if diagonal[m].norm1() <= eps {
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diagonal[m] = N::RealField::zero();
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Self::cancel_horizontal_off_diagonal_elt(
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diagonal,
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off_diagonal,
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u,
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v_t,
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is_upper_diagonal,
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m,
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m + 1,
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);
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if m != 0 {
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Self::cancel_vertical_off_diagonal_elt(
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diagonal,
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off_diagonal,
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u,
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v_t,
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is_upper_diagonal,
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m - 1,
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);
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}
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} else if diagonal[n].norm1() <= eps {
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diagonal[n] = N::RealField::zero();
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Self::cancel_vertical_off_diagonal_elt(
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diagonal,
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off_diagonal,
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u,
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v_t,
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is_upper_diagonal,
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m,
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);
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} else {
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break;
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}
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n -= 1;
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}
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if n == 0 {
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return (0, 0);
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}
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let mut new_start = n - 1;
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while new_start > 0 {
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let m = new_start - 1;
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if off_diagonal[m].norm1() <= eps * (diagonal[new_start].norm1() + diagonal[m].norm1())
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{
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off_diagonal[m] = N::RealField::zero();
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break;
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}
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// FIXME: write a test that enters this case.
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else if diagonal[m].norm1() <= eps {
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diagonal[m] = N::RealField::zero();
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Self::cancel_horizontal_off_diagonal_elt(
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diagonal,
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off_diagonal,
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u,
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v_t,
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is_upper_diagonal,
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m,
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n,
|
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);
|
||
|
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if m != 0 {
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Self::cancel_vertical_off_diagonal_elt(
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diagonal,
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||
off_diagonal,
|
||
u,
|
||
v_t,
|
||
is_upper_diagonal,
|
||
m - 1,
|
||
);
|
||
}
|
||
break;
|
||
}
|
||
|
||
new_start -= 1;
|
||
}
|
||
|
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(new_start, n)
|
||
}
|
||
|
||
// Cancels the i-th off-diagonal element using givens rotations.
|
||
fn cancel_horizontal_off_diagonal_elt(
|
||
diagonal: &mut VectorN<N::RealField, DimMinimum<R, C>>,
|
||
off_diagonal: &mut VectorN<N::RealField, DimDiff<DimMinimum<R, C>, U1>>,
|
||
u: &mut Option<MatrixMN<N, R, DimMinimum<R, C>>>,
|
||
v_t: &mut Option<MatrixMN<N, DimMinimum<R, C>, C>>,
|
||
is_upper_diagonal: bool,
|
||
i: usize,
|
||
end: usize,
|
||
) {
|
||
let mut v = Vector2::new(off_diagonal[i], diagonal[i + 1]);
|
||
off_diagonal[i] = N::RealField::zero();
|
||
|
||
for k in i..end {
|
||
if let Some((rot, norm)) = GivensRotation::cancel_x(&v) {
|
||
let rot = GivensRotation::new_unchecked(rot.c(), N::from_real(rot.s()));
|
||
diagonal[k + 1] = norm;
|
||
|
||
if is_upper_diagonal {
|
||
if let Some(ref mut u) = *u {
|
||
rot.inverse()
|
||
.rotate_rows(&mut u.fixed_columns_with_step_mut::<U2>(i, k - i));
|
||
}
|
||
} else if let Some(ref mut v_t) = *v_t {
|
||
rot.rotate(&mut v_t.fixed_rows_with_step_mut::<U2>(i, k - i));
|
||
}
|
||
|
||
if k + 1 != end {
|
||
v.x = -rot.s().real() * off_diagonal[k + 1];
|
||
v.y = diagonal[k + 2];
|
||
off_diagonal[k + 1] *= rot.c();
|
||
}
|
||
} else {
|
||
break;
|
||
}
|
||
}
|
||
}
|
||
|
||
// Cancels the i-th off-diagonal element using givens rotations.
|
||
fn cancel_vertical_off_diagonal_elt(
|
||
diagonal: &mut VectorN<N::RealField, DimMinimum<R, C>>,
|
||
off_diagonal: &mut VectorN<N::RealField, DimDiff<DimMinimum<R, C>, U1>>,
|
||
u: &mut Option<MatrixMN<N, R, DimMinimum<R, C>>>,
|
||
v_t: &mut Option<MatrixMN<N, DimMinimum<R, C>, C>>,
|
||
is_upper_diagonal: bool,
|
||
i: usize,
|
||
) {
|
||
let mut v = Vector2::new(diagonal[i], off_diagonal[i]);
|
||
off_diagonal[i] = N::RealField::zero();
|
||
|
||
for k in (0..i + 1).rev() {
|
||
if let Some((rot, norm)) = GivensRotation::cancel_y(&v) {
|
||
let rot = GivensRotation::new_unchecked(rot.c(), N::from_real(rot.s()));
|
||
diagonal[k] = norm;
|
||
|
||
if is_upper_diagonal {
|
||
if let Some(ref mut v_t) = *v_t {
|
||
rot.rotate(&mut v_t.fixed_rows_with_step_mut::<U2>(k, i - k));
|
||
}
|
||
} else if let Some(ref mut u) = *u {
|
||
rot.inverse()
|
||
.rotate_rows(&mut u.fixed_columns_with_step_mut::<U2>(k, i - k));
|
||
}
|
||
|
||
if k > 0 {
|
||
v.x = diagonal[k - 1];
|
||
v.y = rot.s().real() * off_diagonal[k - 1];
|
||
off_diagonal[k - 1] *= rot.c();
|
||
}
|
||
} else {
|
||
break;
|
||
}
|
||
}
|
||
}
|
||
|
||
/// Computes the rank of the decomposed matrix, i.e., the number of singular values greater
|
||
/// than `eps`.
|
||
pub fn rank(&self, eps: N::RealField) -> usize {
|
||
assert!(
|
||
eps >= N::RealField::zero(),
|
||
"SVD rank: the epsilon must be non-negative."
|
||
);
|
||
self.singular_values.iter().filter(|e| **e > eps).count()
|
||
}
|
||
|
||
/// Rebuild the original matrix.
|
||
///
|
||
/// This is useful if some of the singular values have been manually modified.
|
||
/// Returns `Err` if the right- and left- singular vectors have not been
|
||
/// computed at construction-time.
|
||
pub fn recompose(self) -> Result<MatrixMN<N, R, C>, &'static str> {
|
||
match (self.u, self.v_t) {
|
||
(Some(mut u), Some(v_t)) => {
|
||
for i in 0..self.singular_values.len() {
|
||
let val = self.singular_values[i];
|
||
u.column_mut(i).scale_mut(val);
|
||
}
|
||
Ok(u * v_t)
|
||
}
|
||
(None, None) => Err("SVD recomposition: U and V^t have not been computed."),
|
||
(None, _) => Err("SVD recomposition: U has not been computed."),
|
||
(_, None) => Err("SVD recomposition: V^t has not been computed."),
|
||
}
|
||
}
|
||
|
||
/// Computes the pseudo-inverse of the decomposed matrix.
|
||
///
|
||
/// Any singular value smaller than `eps` is assumed to be zero.
|
||
/// Returns `Err` if the right- and left- singular vectors have not
|
||
/// been computed at construction-time.
|
||
pub fn pseudo_inverse(mut self, eps: N::RealField) -> Result<MatrixMN<N, C, R>, &'static str>
|
||
where
|
||
DefaultAllocator: Allocator<N, C, R>,
|
||
{
|
||
if eps < N::RealField::zero() {
|
||
Err("SVD pseudo inverse: the epsilon must be non-negative.")
|
||
} else {
|
||
for i in 0..self.singular_values.len() {
|
||
let val = self.singular_values[i];
|
||
|
||
if val > eps {
|
||
self.singular_values[i] = N::RealField::one() / val;
|
||
} else {
|
||
self.singular_values[i] = N::RealField::zero();
|
||
}
|
||
}
|
||
|
||
self.recompose().map(|m| m.adjoint())
|
||
}
|
||
}
|
||
|
||
/// Solves the system `self * x = b` where `self` is the decomposed matrix and `x` the unknown.
|
||
///
|
||
/// Any singular value smaller than `eps` is assumed to be zero.
|
||
/// Returns `Err` if the singular vectors `U` and `V` have not been computed.
|
||
// FIXME: make this more generic wrt the storage types and the dimensions for `b`.
|
||
pub fn solve<R2: Dim, C2: Dim, S2>(
|
||
&self,
|
||
b: &Matrix<N, R2, C2, S2>,
|
||
eps: N::RealField,
|
||
) -> Result<MatrixMN<N, C, C2>, &'static str>
|
||
where
|
||
S2: Storage<N, R2, C2>,
|
||
DefaultAllocator: Allocator<N, C, C2> + Allocator<N, DimMinimum<R, C>, C2>,
|
||
ShapeConstraint: SameNumberOfRows<R, R2>,
|
||
{
|
||
if eps < N::RealField::zero() {
|
||
Err("SVD solve: the epsilon must be non-negative.")
|
||
} else {
|
||
match (&self.u, &self.v_t) {
|
||
(Some(u), Some(v_t)) => {
|
||
let mut ut_b = u.ad_mul(b);
|
||
|
||
for j in 0..ut_b.ncols() {
|
||
let mut col = ut_b.column_mut(j);
|
||
|
||
for i in 0..self.singular_values.len() {
|
||
let val = self.singular_values[i];
|
||
if val > eps {
|
||
col[i] = col[i].unscale(val);
|
||
} else {
|
||
col[i] = N::zero();
|
||
}
|
||
}
|
||
}
|
||
|
||
Ok(v_t.ad_mul(&ut_b))
|
||
}
|
||
(None, None) => Err("SVD solve: U and V^t have not been computed."),
|
||
(None, _) => Err("SVD solve: U has not been computed."),
|
||
(_, None) => Err("SVD solve: V^t has not been computed."),
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
impl<N: ComplexField, R: DimMin<C>, C: Dim, S: Storage<N, R, C>> Matrix<N, R, C, S>
|
||
where
|
||
DimMinimum<R, C>: DimSub<U1>, // for Bidiagonal.
|
||
DefaultAllocator: Allocator<N, R, C>
|
||
+ Allocator<N, C>
|
||
+ Allocator<N, R>
|
||
+ Allocator<N, DimDiff<DimMinimum<R, C>, U1>>
|
||
+ Allocator<N, DimMinimum<R, C>, C>
|
||
+ Allocator<N, R, DimMinimum<R, C>>
|
||
+ Allocator<N, DimMinimum<R, C>>
|
||
+ Allocator<N::RealField, DimMinimum<R, C>>
|
||
+ Allocator<N::RealField, DimDiff<DimMinimum<R, C>, U1>>,
|
||
{
|
||
/// Computes the Singular Value Decomposition using implicit shift.
|
||
pub fn svd(self, compute_u: bool, compute_v: bool) -> SVD<N, R, C> {
|
||
SVD::new(self.into_owned(), compute_u, compute_v)
|
||
}
|
||
|
||
/// Attempts to compute the Singular Value Decomposition of `matrix` using implicit shift.
|
||
///
|
||
/// # Arguments
|
||
///
|
||
/// * `compute_u` − set this to `true` to enable the computation of left-singular vectors.
|
||
/// * `compute_v` − set this to `true` to enable the computation of left-singular vectors.
|
||
/// * `eps` − tolerance used to determine when a value converged to 0.
|
||
/// * `max_niter` − maximum total number of iterations performed by the algorithm. If this
|
||
/// number of iteration is exceeded, `None` is returned. If `niter == 0`, then the algorithm
|
||
/// continues indefinitely until convergence.
|
||
pub fn try_svd(
|
||
self,
|
||
compute_u: bool,
|
||
compute_v: bool,
|
||
eps: N::RealField,
|
||
max_niter: usize,
|
||
) -> Option<SVD<N, R, C>> {
|
||
SVD::try_new(self.into_owned(), compute_u, compute_v, eps, max_niter)
|
||
}
|
||
|
||
/// Computes the singular values of this matrix.
|
||
pub fn singular_values(&self) -> VectorN<N::RealField, DimMinimum<R, C>> {
|
||
SVD::new(self.clone_owned(), false, false).singular_values
|
||
}
|
||
|
||
/// Computes the rank of this matrix.
|
||
///
|
||
/// All singular values below `eps` are considered equal to 0.
|
||
pub fn rank(&self, eps: N::RealField) -> usize {
|
||
let svd = SVD::new(self.clone_owned(), false, false);
|
||
svd.rank(eps)
|
||
}
|
||
|
||
/// Computes the pseudo-inverse of this matrix.
|
||
///
|
||
/// All singular values below `eps` are considered equal to 0.
|
||
pub fn pseudo_inverse(self, eps: N::RealField) -> Result<MatrixMN<N, C, R>, &'static str>
|
||
where
|
||
DefaultAllocator: Allocator<N, C, R>,
|
||
{
|
||
SVD::new(self.clone_owned(), true, true).pseudo_inverse(eps)
|
||
}
|
||
}
|
||
|
||
// Explicit formulae inspired from the paper "Computing the Singular Values of 2-by-2 Complex
|
||
// Matrices", Sanzheng Qiao and Xiaohong Wang.
|
||
// http://www.cas.mcmaster.ca/sqrl/papers/sqrl5.pdf
|
||
fn compute_2x2_uptrig_svd<N: RealField>(
|
||
m11: N,
|
||
m12: N,
|
||
m22: N,
|
||
compute_u: bool,
|
||
compute_v: bool,
|
||
) -> (
|
||
Option<GivensRotation<N>>,
|
||
Vector2<N>,
|
||
Option<GivensRotation<N>>,
|
||
) {
|
||
let two: N::RealField = crate::convert(2.0f64);
|
||
let half: N::RealField = crate::convert(0.5f64);
|
||
|
||
let denom = (m11 + m22).hypot(m12) + (m11 - m22).hypot(m12);
|
||
|
||
// NOTE: v1 is the singular value that is the closest to m22.
|
||
// This prevents cancellation issues when constructing the vector `csv` below. If we chose
|
||
// otherwise, we would have v1 ~= m11 when m12 is small. This would cause catastrophic
|
||
// cancellation on `v1 * v1 - m11 * m11` below.
|
||
let mut v1 = m11 * m22 * two / denom;
|
||
let mut v2 = half * denom;
|
||
|
||
let mut u = None;
|
||
let mut v_t = None;
|
||
|
||
if compute_u || compute_v {
|
||
let (csv, sgn_v) = GivensRotation::new(m11 * m12, v1 * v1 - m11 * m11);
|
||
v1 *= sgn_v;
|
||
v2 *= sgn_v;
|
||
|
||
if compute_v {
|
||
v_t = Some(csv);
|
||
}
|
||
|
||
if compute_u {
|
||
let cu = (m11.scale(csv.c()) + m12 * csv.s()) / v1;
|
||
let su = (m22 * csv.s()) / v1;
|
||
let (csu, sgn_u) = GivensRotation::new(cu, su);
|
||
|
||
v1 *= sgn_u;
|
||
v2 *= sgn_u;
|
||
u = Some(csu);
|
||
}
|
||
}
|
||
|
||
(u, Vector2::new(v1, v2), v_t)
|
||
}
|