L &gt;= 0.

  A       (input/output) DOUBLE PRECISION array, dimension (LDA,M)
          On entry, the leading N-by-M part of this array must
          contain the matrix A. The elements corresponding to the
          zero MIN(N,P)-by-P upper trapezoidal/triangular part
          (if P &gt; 0) are not referenced.
          On exit, the elements on and below the diagonal of this
          array contain the N-by-MIN(N,M) lower trapezoidal matrix
          L (L is lower triangular, if N &lt;= M) of the LQ
    