Find the Recurrence relation for $q_n$ given the following condition:












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Let $q_n$ denote the number of strings of length $n$ (formed from digits 0,1,2,3) which have even number of $2$'s. set up a recurrence relation for $q_n$.










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    $begingroup$


    Let $q_n$ denote the number of strings of length $n$ (formed from digits 0,1,2,3) which have even number of $2$'s. set up a recurrence relation for $q_n$.










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      $begingroup$


      Let $q_n$ denote the number of strings of length $n$ (formed from digits 0,1,2,3) which have even number of $2$'s. set up a recurrence relation for $q_n$.










      share|cite|improve this question











      $endgroup$




      Let $q_n$ denote the number of strings of length $n$ (formed from digits 0,1,2,3) which have even number of $2$'s. set up a recurrence relation for $q_n$.







      discrete-mathematics recurrence-relations generating-functions






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      edited Dec 10 '18 at 9:19







      Cosmic

















      asked Dec 10 '18 at 8:54









      CosmicCosmic

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      8810






















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          $begingroup$

          Indeed it can be defined by two recurrence. Suppose $p_n$ is the number of strings which have odd 2's. Now we have:
          $$q_n = 3q_{n-1} + p_{n-1}$$
          $$p_n = q_{n-1} + 3 p_{n-1}$$



          Now we can unified them by matrix operation by $T_n = begin{bmatrix}q_n \ p_n end{bmatrix}$:



          $$T_n=begin{bmatrix}3 & 0 \ 0 & 1 end{bmatrix}T_{n-1}+begin{bmatrix}0 & 1 \ 3 & 0 end{bmatrix}T_{n-1}=begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}T_{n-1}.$$



          Now we can say $T_n = begin{bmatrix}q_n \ p_n end{bmatrix} = begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}^{n-1}T_1$. We can compute that $T_1 = begin{bmatrix}3 \ 1 end{bmatrix}$, and
          $$T_n = begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}^{n-1}begin{bmatrix}3 \ 1 end{bmatrix}$$






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            $begingroup$

            Indeed it can be defined by two recurrence. Suppose $p_n$ is the number of strings which have odd 2's. Now we have:
            $$q_n = 3q_{n-1} + p_{n-1}$$
            $$p_n = q_{n-1} + 3 p_{n-1}$$



            Now we can unified them by matrix operation by $T_n = begin{bmatrix}q_n \ p_n end{bmatrix}$:



            $$T_n=begin{bmatrix}3 & 0 \ 0 & 1 end{bmatrix}T_{n-1}+begin{bmatrix}0 & 1 \ 3 & 0 end{bmatrix}T_{n-1}=begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}T_{n-1}.$$



            Now we can say $T_n = begin{bmatrix}q_n \ p_n end{bmatrix} = begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}^{n-1}T_1$. We can compute that $T_1 = begin{bmatrix}3 \ 1 end{bmatrix}$, and
            $$T_n = begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}^{n-1}begin{bmatrix}3 \ 1 end{bmatrix}$$






            share|cite|improve this answer











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              0












              $begingroup$

              Indeed it can be defined by two recurrence. Suppose $p_n$ is the number of strings which have odd 2's. Now we have:
              $$q_n = 3q_{n-1} + p_{n-1}$$
              $$p_n = q_{n-1} + 3 p_{n-1}$$



              Now we can unified them by matrix operation by $T_n = begin{bmatrix}q_n \ p_n end{bmatrix}$:



              $$T_n=begin{bmatrix}3 & 0 \ 0 & 1 end{bmatrix}T_{n-1}+begin{bmatrix}0 & 1 \ 3 & 0 end{bmatrix}T_{n-1}=begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}T_{n-1}.$$



              Now we can say $T_n = begin{bmatrix}q_n \ p_n end{bmatrix} = begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}^{n-1}T_1$. We can compute that $T_1 = begin{bmatrix}3 \ 1 end{bmatrix}$, and
              $$T_n = begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}^{n-1}begin{bmatrix}3 \ 1 end{bmatrix}$$






              share|cite|improve this answer











              $endgroup$
















                0












                0








                0





                $begingroup$

                Indeed it can be defined by two recurrence. Suppose $p_n$ is the number of strings which have odd 2's. Now we have:
                $$q_n = 3q_{n-1} + p_{n-1}$$
                $$p_n = q_{n-1} + 3 p_{n-1}$$



                Now we can unified them by matrix operation by $T_n = begin{bmatrix}q_n \ p_n end{bmatrix}$:



                $$T_n=begin{bmatrix}3 & 0 \ 0 & 1 end{bmatrix}T_{n-1}+begin{bmatrix}0 & 1 \ 3 & 0 end{bmatrix}T_{n-1}=begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}T_{n-1}.$$



                Now we can say $T_n = begin{bmatrix}q_n \ p_n end{bmatrix} = begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}^{n-1}T_1$. We can compute that $T_1 = begin{bmatrix}3 \ 1 end{bmatrix}$, and
                $$T_n = begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}^{n-1}begin{bmatrix}3 \ 1 end{bmatrix}$$






                share|cite|improve this answer











                $endgroup$



                Indeed it can be defined by two recurrence. Suppose $p_n$ is the number of strings which have odd 2's. Now we have:
                $$q_n = 3q_{n-1} + p_{n-1}$$
                $$p_n = q_{n-1} + 3 p_{n-1}$$



                Now we can unified them by matrix operation by $T_n = begin{bmatrix}q_n \ p_n end{bmatrix}$:



                $$T_n=begin{bmatrix}3 & 0 \ 0 & 1 end{bmatrix}T_{n-1}+begin{bmatrix}0 & 1 \ 3 & 0 end{bmatrix}T_{n-1}=begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}T_{n-1}.$$



                Now we can say $T_n = begin{bmatrix}q_n \ p_n end{bmatrix} = begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}^{n-1}T_1$. We can compute that $T_1 = begin{bmatrix}3 \ 1 end{bmatrix}$, and
                $$T_n = begin{bmatrix}3 & 1 \ 3 & 1 end{bmatrix}^{n-1}begin{bmatrix}3 \ 1 end{bmatrix}$$







                share|cite|improve this answer














                share|cite|improve this answer



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                edited Dec 10 '18 at 9:57

























                answered Dec 10 '18 at 9:49









                OmGOmG

                2,502822




                2,502822






























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