sla.qr              package:RScaLAPACK              R Documentation

_T_h_e _Q_R _D_e_c_o_m_p_o_s_i_t_i_o_n _o_f _a _M_a_t_r_i_x (_U_s_i_n_g _S_c_a_L_A_P_A_C_K)

_D_e_s_c_r_i_p_t_i_o_n:

     The function 'sla.qr' computes the QR decomposition of a matrix
     using the ScaLAPACK library routine PDGEQRF.

_U_s_a_g_e:

     sla.qr(A, NPROWS, NPCOLS, MB, RFLAG, SPAWN)

_A_r_g_u_m_e_n_t_s:

       A: A numeric matrix whose QR decomposition is to be computed.

  NPROWS: Number of Process Rows in the Process Grid. 

  NPCOLS: Number of Process Cols in the Process Grid. 

      MB: Block Size. 

   RFLAG: Flag saying whether the Process Grid should be released after
          computation.

   SPAWN: Flag saying whether a new Process Grid should be spawned.

_D_e_t_a_i_l_s:

     If the number of processor rows and columns are both zero, one
     processor is used.  If the number of processor rows is nonzero and
     the number of processor columns is zero, then the processor rows
     is taken to be a  number of processors, and a grid is made
     accordingly.

_V_a_l_u_e:

     The QR decomposition of the matrix as computed by PDGEQRF is
     returned. 

      qr: a matrix with the same dimensions as 'A'. The upper triangle
          contains the *R* of the decomposition and the lower triangle
          contains a representation of the *Q* of the decomposition
          (stored in the LAPACK compact form).

   qraux: a vector of length 'min(ncol(A),nrow(A)' which contains
          information needed to extract *Q*.

    rank: the length of vector *qraux*.

_R_e_f_e_r_e_n_c_e_s:

     <URL: http://mathworld.wolfram.com/QRDecomposition.html>

     <URL: http://www.netlib.org/scalapack/>

_S_e_e _A_l_s_o:

     'qr' for the normal solving function.

_E_x_a_m_p_l_e_s:

     library(RScaLAPACK)
     rnorm(100)->x
     dim(x)=c(10,10)
     sla.qr(x)

