code: public static ZMatrixRMaj identity(int width ) {
          ZMatrixRMaj A = new ZMatrixRMaj(width,width);
  
          for (int i = 0; i < width; i++) {
              A.set(i,i,1,0);
          }
  
          return A;
      }
docs: <p>
  Creates an identity matrix of the specified size.<br>
  <br>
  a<sub>ij</sub> = 0+0i   if i &ne; j<br>
  a<sub>ij</sub> = 1+0i   if i = j<br>
  </p>
  
  @param width The width and height of the identity matrix.
  @return A new instance of an identity matrix.