text: #include "cs.h"
  /* C = A(p,p) where A and C are symmetric the upper part stored; pinv not p */
  cs *cs_symperm (const cs *A, const csi *pinv, csi values)
  {
      csi i, j, p, q, i2, j2, n, *Ap, *Ai, *Cp, *Ci, *w ;
      double *Cx, *Ax ;
      cs *C ;
      if (!CS_CSC (A)) return (NULL) ;                    /* check inputs */
      n = A->n ; Ap = A->p ; Ai = A->i ; Ax = A->x ;
      C = cs_spalloc (n, n, Ap [n], values && (Ax != NULL), 0) ; /* alloc result*/
      w = cs_calloc (n, sizeof (csi)) ;                   /* get workspace */
      if (!C || !w) return (cs_done (C, w, NULL, 0)) ;    /* out of memory */
      Cp = C->p ; Ci = C->i ; Cx = C->x ;
      for (j = 0 ; j < n ; j++)           /* count entries in each column of C */
      {
          j2 = pinv ? pinv [j] : j ;      /* column j of A is column j2 of C */
          for (p = Ap [j] ; p < Ap [j+1] ; p++)
          {
              i = Ai [p] ;
              if (i > j) continue ;       /* skip lower triangular part of A */
              i2 = pinv ? pinv [i] : i ;  /* row i of A is row i2 of C */
              w [CS_MAX (i2, j2)]++ ;     /* column count of C */
          }
      }
      cs_cumsum (Cp, w, n) ;              /* compute column pointers of C */
      for (j = 0 ; j < n ; j++)
      {
          j2 = pinv ? pinv [j] : j ;      /* column j of A is column j2 of C */
          for (p = Ap [j] ; p < Ap [j+1] ; p++)
          {
              i = Ai [p] ;
              if (i > j) continue ;       /* skip lower triangular part of A*/
              i2 = pinv ? pinv [i] : i ;  /* row i of A is row i2 of C */
              Ci [q = w [CS_MAX (i2, j2)]++] = CS_MIN (i2, j2) ;
              if (Cx) Cx [q] = Ax [p] ;
          }
      }
      return (cs_done (C, w, NULL, 1)) ;  /* success; free workspace, return C */
  }
  
  /* C = A(p,p) where A and C are symmetric the full matrix stored; pinv not p */
  cs *is_symperm (const cs *A, const csi *pinv, csi values)
  {
      csi i, j, p, q, i2, j2, n, *Ap, *Ai, *Cp, *Ci, *w ;
      double *Cx, *Ax ;
      cs *C ;
      if (!CS_CSC (A)) return (NULL) ;                    /* check inputs */
      n = A->n ; Ap = A->p ; Ai = A->i ; Ax = A->x ;
      C = cs_spalloc (n, n, Ap [n], values && (Ax != NULL), 0) ; /* alloc result*/
      w = cs_calloc (n, sizeof (csi)) ;                   /* get workspace */
      if (!C || !w) return (cs_done (C, w, NULL, 0)) ;    /* out of memory */
      Cp = C->p ; Ci = C->i ; Cx = C->x ;
  
      for (j = 0 ; j < n ; j++)           /* count entries in each column of C */
      {
          j2 = pinv ? pinv [j] : j ;      /* column j of A is column j2 of C */
          for (p = Ap [j] ; p < Ap [j+1] ; p++)
          {
              i = Ai [p] ; 
              i2 = pinv ? pinv [i] : i ;  /* row i of A is row i2 of C */
              if (i > j)
                  w [CS_MIN (i2, j2)]++ ; /* column count of C */
              else
                  w [CS_MAX (i2, j2)]++ ; /* column count of C */
          }
      }
      cs_cumsum (Cp, w, n) ;              /* compute column pointers of C */
      for (j = 0 ; j < n ; j++)
      {
          j2 = pinv ? pinv [j] : j ;      /* column j of A is column j2 of C */
          for (p = Ap [j] ; p < Ap [j+1] ; p++)
          {
              i = Ai [p] ;
              i2 = pinv ? pinv [i] : i ;  /* row i of A is row i2 of C */
              if (i > j)
                  Ci [q = w [CS_MIN (i2, j2)]++] = CS_MAX (i2, j2) ;
              else
                  Ci [q = w [CS_MAX (i2, j2)]++] = CS_MIN (i2, j2) ;
              if (Cx) Cx [q] = Ax [p] ;
          }
      }
      return (cs_done (C, w, NULL, 1)) ;  /* success; free workspace, return C */
  }