 Usage:  beta = eivlinearinstrvec(x,w,y)  
 
 Input:

  x                      n x 1 matrix, the design variables 
                         
  w                      n x 1 matrix, the instrumental variables 
                         
  y                      n x 1 matrix, the response 
                         
 Output:

  beta                   vector, the estimate 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
