 Usage:  {beta,bv} = reca(y,w,z,su2)  
 
 Input:

  y                      n x 1 matrix, the design variables 
                         
  w                      n x 1 matrix 
                         
  z                      n x 1 matrix 
                         
  su2                    the variance of the measurement error 
                         
 Output:

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