Compute eigen values using iterative shifted QR decomposition algorithm as * follows: * 1. Use last diagonal element of A as eigen value approximation \f$c\f$ * 2. Shift diagonals of matrix \f$A' = A - cI\f$ * 3. Decompose matrix \f$A'=QR\f$ * 4. Compute next approximation \f$A'_1 = RQ \f$ * 5. Shift diagonals back \f$A_1 = A'_1 + cI\f$ * 6. Termination condition check: last element below d