Skip to main content
`Ctrl`+`K`
scipy.linalg.

# qr_multiply

scipy.linalg.qr_multiply(a, c, mode='right', pivoting=False, conjugate=False, overwrite_a=False, overwrite_c=False)

  Calculate the QR decomposition and multiply Q with a matrix.

  Calculate the decomposition `A = Q R` where Q is unitary/orthogonal and R upper triangular. Multiply Q with a vector or a matrix c.

  The documentation is written assuming array arguments are of specified “core” shapes. However, array argument(s) of this function may have additional “batch” dimensions prepended to the core shape. In this case, the array is treated as a batch of lower-dimensional slices; see Batched Linear Operations for details.

  Parameters:
    a(M, N), array_like

      Input array

    carray_like

      Input array to be multiplied by `q`.

    mode{‘left’, ‘right’}, optional

      `Q @ c` is returned if mode is ‘left’, `c @ Q` is returned if mode is ‘right’. The shape of c must be appropriate for the matrix multiplications, if mode is ‘left’, `min(a.shape) == c.shape[0]`, if mode is ‘right’, `a.shape[0] == c.shape[1]`.

    pivotingbool, optional

      Whether or not factorization should include pivoting for rank-revealing qr decomposition, see the documentation of qr.

    conjugatebool, optional

      Whether Q should be complex-conjugated. This might be faster than explicit conjugation.

    overwrite_abool, optional

      Whether data in a is overwritten (may improve performance)

    overwrite_cbool, optional

      Whether data in c is overwritten (may improve performance). If this is used, c must be big enough to keep the result, i.e. `c.shape[0]` = `a.shape[0]` if mode is ‘left’.

  Returns:
    CQndarray

      The product of `Q` and `c`.

    R(K, N), ndarray

      R array of the resulting QR factorization where `K = min(M, N)`.

    P(N,) ndarray

      Integer pivot array. Only returned when `pivoting=True`.

  Raises:
    LinAlgError

      Raised if QR decomposition fails.

  Notes

  This is an interface to the LAPACK routines `?GEQRF`, `?ORMQR`, `?UNMQR`, and `?GEQP3`.

  Added in version 0.11.0.

  Examples

      >>> import numpy as np
      >>> from scipy.linalg import qr_multiply, qr
      >>> A = np.array([[1, 3, 3], [2, 3, 2], [2, 3, 3], [1, 3, 2]])
      >>> qc, r1, piv1 = qr_multiply(A, 2*np.eye(4), pivoting=1)
      >>> qc
      array([[-1.,  1., -1.],
             [-1., -1.,  1.],
             [-1., -1., -1.],
             [-1.,  1.,  1.]])
      >>> r1
      array([[-6., -3., -5.            ],
             [ 0., -1., -1.11022302e-16],
             [ 0.,  0., -1.            ]])
      >>> piv1
      array([1, 0, 2], dtype=int32)
      >>> q2, r2, piv2 = qr(A, mode='economic', pivoting=1)
      >>> np.allclose(2*q2 - qc, np.zeros((4, 3)))
      True