 Usage:  bd = chold(x,l)  
 
 Input:

  x                      n x n matrix, the input matrix 
                         
  l                      scalar, the number of lower non-zero subdiagonals including 
                         the diagonal 
                         
 Output:

  bd                     n x n matrix, see note 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
