 Usage:  dx = diff(x)  
 
 Input:

  x                      array, d1 x d2 x ... x dn 
                         
 Output:

  dx                     array, (d1-1) x d2 x ... x dn, first 
                         differences along the rows of x. 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
