On a special kind of $6$-dimensional vector subspace of $mathbb C^9$












3












$begingroup$


Let $V subseteq mathbb C^9$ be a vector subspace of dimension $6$. Suppose that there exists $A,B in M_{3 times 6} (mathbb C)$ such that



$V={(x_1,...,x_9)in mathbb C^9 : (x_3,x_6,x_9)^T = A (x_1,x_2,x_4,x_5,x_7,x_8)^T }={(x_1,...,x_9)in mathbb C^9 : (x_3,x_6,x_9)^T = B(x_1,x_2,x_4,x_5,x_7,x_8)^T }$



; then is it true that $A=B$ ?










share|cite|improve this question









$endgroup$

















    3












    $begingroup$


    Let $V subseteq mathbb C^9$ be a vector subspace of dimension $6$. Suppose that there exists $A,B in M_{3 times 6} (mathbb C)$ such that



    $V={(x_1,...,x_9)in mathbb C^9 : (x_3,x_6,x_9)^T = A (x_1,x_2,x_4,x_5,x_7,x_8)^T }={(x_1,...,x_9)in mathbb C^9 : (x_3,x_6,x_9)^T = B(x_1,x_2,x_4,x_5,x_7,x_8)^T }$



    ; then is it true that $A=B$ ?










    share|cite|improve this question









    $endgroup$















      3












      3








      3


      1



      $begingroup$


      Let $V subseteq mathbb C^9$ be a vector subspace of dimension $6$. Suppose that there exists $A,B in M_{3 times 6} (mathbb C)$ such that



      $V={(x_1,...,x_9)in mathbb C^9 : (x_3,x_6,x_9)^T = A (x_1,x_2,x_4,x_5,x_7,x_8)^T }={(x_1,...,x_9)in mathbb C^9 : (x_3,x_6,x_9)^T = B(x_1,x_2,x_4,x_5,x_7,x_8)^T }$



      ; then is it true that $A=B$ ?










      share|cite|improve this question









      $endgroup$




      Let $V subseteq mathbb C^9$ be a vector subspace of dimension $6$. Suppose that there exists $A,B in M_{3 times 6} (mathbb C)$ such that



      $V={(x_1,...,x_9)in mathbb C^9 : (x_3,x_6,x_9)^T = A (x_1,x_2,x_4,x_5,x_7,x_8)^T }={(x_1,...,x_9)in mathbb C^9 : (x_3,x_6,x_9)^T = B(x_1,x_2,x_4,x_5,x_7,x_8)^T }$



      ; then is it true that $A=B$ ?







      linear-algebra matrices






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      asked Dec 13 '18 at 8:38









      user521337user521337

      1,1551417




      1,1551417






















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          $begingroup$

          Yes, this is true. Up to the numbering of coordinates, you just write $V={(y,Ay):yinmathbb C^6}$ and $V={(y,By):yinmathbb C^6}$. Now if you insert the basis vectors $e_1,dots,e_6$, you readily see that the vectors $(e_1,Ae_1),dots,(e_6,Ae_6)$ are linearly indent. Since $dim(V)=6$, they have to be a basis of $V$. But this implies that any element $vin V$ is determined by the coordinates $v_1,dots,v_6$, so given $yinmathbb C^6$, there is at most one $zinmathbb C^3$ such that $(y,z)in V$, and this implies $A=B$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            thanks ... could you also please take a look at the related question math.stackexchange.com/questions/3037774/… ?
            $endgroup$
            – user521337
            Dec 13 '18 at 23:58











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          1 Answer
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          1 Answer
          1






          active

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          active

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          active

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          0












          $begingroup$

          Yes, this is true. Up to the numbering of coordinates, you just write $V={(y,Ay):yinmathbb C^6}$ and $V={(y,By):yinmathbb C^6}$. Now if you insert the basis vectors $e_1,dots,e_6$, you readily see that the vectors $(e_1,Ae_1),dots,(e_6,Ae_6)$ are linearly indent. Since $dim(V)=6$, they have to be a basis of $V$. But this implies that any element $vin V$ is determined by the coordinates $v_1,dots,v_6$, so given $yinmathbb C^6$, there is at most one $zinmathbb C^3$ such that $(y,z)in V$, and this implies $A=B$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            thanks ... could you also please take a look at the related question math.stackexchange.com/questions/3037774/… ?
            $endgroup$
            – user521337
            Dec 13 '18 at 23:58
















          0












          $begingroup$

          Yes, this is true. Up to the numbering of coordinates, you just write $V={(y,Ay):yinmathbb C^6}$ and $V={(y,By):yinmathbb C^6}$. Now if you insert the basis vectors $e_1,dots,e_6$, you readily see that the vectors $(e_1,Ae_1),dots,(e_6,Ae_6)$ are linearly indent. Since $dim(V)=6$, they have to be a basis of $V$. But this implies that any element $vin V$ is determined by the coordinates $v_1,dots,v_6$, so given $yinmathbb C^6$, there is at most one $zinmathbb C^3$ such that $(y,z)in V$, and this implies $A=B$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            thanks ... could you also please take a look at the related question math.stackexchange.com/questions/3037774/… ?
            $endgroup$
            – user521337
            Dec 13 '18 at 23:58














          0












          0








          0





          $begingroup$

          Yes, this is true. Up to the numbering of coordinates, you just write $V={(y,Ay):yinmathbb C^6}$ and $V={(y,By):yinmathbb C^6}$. Now if you insert the basis vectors $e_1,dots,e_6$, you readily see that the vectors $(e_1,Ae_1),dots,(e_6,Ae_6)$ are linearly indent. Since $dim(V)=6$, they have to be a basis of $V$. But this implies that any element $vin V$ is determined by the coordinates $v_1,dots,v_6$, so given $yinmathbb C^6$, there is at most one $zinmathbb C^3$ such that $(y,z)in V$, and this implies $A=B$.






          share|cite|improve this answer









          $endgroup$



          Yes, this is true. Up to the numbering of coordinates, you just write $V={(y,Ay):yinmathbb C^6}$ and $V={(y,By):yinmathbb C^6}$. Now if you insert the basis vectors $e_1,dots,e_6$, you readily see that the vectors $(e_1,Ae_1),dots,(e_6,Ae_6)$ are linearly indent. Since $dim(V)=6$, they have to be a basis of $V$. But this implies that any element $vin V$ is determined by the coordinates $v_1,dots,v_6$, so given $yinmathbb C^6$, there is at most one $zinmathbb C^3$ such that $(y,z)in V$, and this implies $A=B$.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Dec 13 '18 at 10:46









          Andreas CapAndreas Cap

          11.2k923




          11.2k923












          • $begingroup$
            thanks ... could you also please take a look at the related question math.stackexchange.com/questions/3037774/… ?
            $endgroup$
            – user521337
            Dec 13 '18 at 23:58


















          • $begingroup$
            thanks ... could you also please take a look at the related question math.stackexchange.com/questions/3037774/… ?
            $endgroup$
            – user521337
            Dec 13 '18 at 23:58
















          $begingroup$
          thanks ... could you also please take a look at the related question math.stackexchange.com/questions/3037774/… ?
          $endgroup$
          – user521337
          Dec 13 '18 at 23:58




          $begingroup$
          thanks ... could you also please take a look at the related question math.stackexchange.com/questions/3037774/… ?
          $endgroup$
          – user521337
          Dec 13 '18 at 23:58


















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