Big O /Right or wrong?Prove $O(x)+O(x^2)=O(x^2)$ (Big O Notation)$f(n) in o(g(n))$ and $g(n) in o(f(n))$Prove or disapprove the statement: $f(n)=Theta(f(fracn2))$Prove that $fracn^22 - 3n = Theta(n^2)$Algorithm Theta Notation : How constant $c_2 geq 1/2$ is derived from the inequality $c_1 leq 1/2 - 3/n leq c_2$How to prove Big Theta on polynomial function?Prove $O(n+log(n)) subset O(n cdot log(n))$How to prove big theta inequality?Asymptotic notations - Big Omega ProofStrange big-O notation?

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Big O /Right or wrong?


Prove $O(x)+O(x^2)=O(x^2)$ (Big O Notation)$f(n) in o(g(n))$ and $g(n) in o(f(n))$Prove or disapprove the statement: $f(n)=Theta(f(fracn2))$Prove that $fracn^22 - 3n = Theta(n^2)$Algorithm Theta Notation : How constant $c_2 geq 1/2$ is derived from the inequality $c_1 leq 1/2 - 3/n leq c_2$How to prove Big Theta on polynomial function?Prove $O(n+log(n)) subset O(n cdot log(n))$How to prove big theta inequality?Asymptotic notations - Big Omega ProofStrange big-O notation?













4












$begingroup$


I have to decide, wether the following theorem is right or wrong.
There are functions, that satisfy the following conditions:



$ f(n) in mathcalO(h(n)) $ and $ g(n) in mathcalO(h(n))$



Now it should hold: $$ fracf(n)g(n) =mathcalO(1) $$



By definition I get: $f(n) leq c_1 cdot h(n) forall ngeq N$ and $g(n) leq c_2 cdot h(n) forall ngeq N'$



So, $$ fracf(n)g(n) = fracc_1c_2 cdot 1 forall ngeq maxN,N'$$



I'm not sure. g(n) could be 0. What do you think?










share|cite|improve this question









$endgroup$







  • 3




    $begingroup$
    I don't understand why you went from saying f and g are elements of O(something) to f/g being equal to O(1). O(1) is a set, and f/g is a function, so surely the question is whether it is an element of O(1), right? Was this a typo? Can you explain the question more clearly?
    $endgroup$
    – Eric Lippert
    Apr 26 at 15:13
















4












$begingroup$


I have to decide, wether the following theorem is right or wrong.
There are functions, that satisfy the following conditions:



$ f(n) in mathcalO(h(n)) $ and $ g(n) in mathcalO(h(n))$



Now it should hold: $$ fracf(n)g(n) =mathcalO(1) $$



By definition I get: $f(n) leq c_1 cdot h(n) forall ngeq N$ and $g(n) leq c_2 cdot h(n) forall ngeq N'$



So, $$ fracf(n)g(n) = fracc_1c_2 cdot 1 forall ngeq maxN,N'$$



I'm not sure. g(n) could be 0. What do you think?










share|cite|improve this question









$endgroup$







  • 3




    $begingroup$
    I don't understand why you went from saying f and g are elements of O(something) to f/g being equal to O(1). O(1) is a set, and f/g is a function, so surely the question is whether it is an element of O(1), right? Was this a typo? Can you explain the question more clearly?
    $endgroup$
    – Eric Lippert
    Apr 26 at 15:13














4












4








4


1



$begingroup$


I have to decide, wether the following theorem is right or wrong.
There are functions, that satisfy the following conditions:



$ f(n) in mathcalO(h(n)) $ and $ g(n) in mathcalO(h(n))$



Now it should hold: $$ fracf(n)g(n) =mathcalO(1) $$



By definition I get: $f(n) leq c_1 cdot h(n) forall ngeq N$ and $g(n) leq c_2 cdot h(n) forall ngeq N'$



So, $$ fracf(n)g(n) = fracc_1c_2 cdot 1 forall ngeq maxN,N'$$



I'm not sure. g(n) could be 0. What do you think?










share|cite|improve this question









$endgroup$




I have to decide, wether the following theorem is right or wrong.
There are functions, that satisfy the following conditions:



$ f(n) in mathcalO(h(n)) $ and $ g(n) in mathcalO(h(n))$



Now it should hold: $$ fracf(n)g(n) =mathcalO(1) $$



By definition I get: $f(n) leq c_1 cdot h(n) forall ngeq N$ and $g(n) leq c_2 cdot h(n) forall ngeq N'$



So, $$ fracf(n)g(n) = fracc_1c_2 cdot 1 forall ngeq maxN,N'$$



I'm not sure. g(n) could be 0. What do you think?







real-analysis asymptotics






share|cite|improve this question













share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked Apr 26 at 10:54









Leon1998Leon1998

10210




10210







  • 3




    $begingroup$
    I don't understand why you went from saying f and g are elements of O(something) to f/g being equal to O(1). O(1) is a set, and f/g is a function, so surely the question is whether it is an element of O(1), right? Was this a typo? Can you explain the question more clearly?
    $endgroup$
    – Eric Lippert
    Apr 26 at 15:13













  • 3




    $begingroup$
    I don't understand why you went from saying f and g are elements of O(something) to f/g being equal to O(1). O(1) is a set, and f/g is a function, so surely the question is whether it is an element of O(1), right? Was this a typo? Can you explain the question more clearly?
    $endgroup$
    – Eric Lippert
    Apr 26 at 15:13








3




3




$begingroup$
I don't understand why you went from saying f and g are elements of O(something) to f/g being equal to O(1). O(1) is a set, and f/g is a function, so surely the question is whether it is an element of O(1), right? Was this a typo? Can you explain the question more clearly?
$endgroup$
– Eric Lippert
Apr 26 at 15:13





$begingroup$
I don't understand why you went from saying f and g are elements of O(something) to f/g being equal to O(1). O(1) is a set, and f/g is a function, so surely the question is whether it is an element of O(1), right? Was this a typo? Can you explain the question more clearly?
$endgroup$
– Eric Lippert
Apr 26 at 15:13











2 Answers
2






active

oldest

votes


















12












$begingroup$

You can't go from $f leqslant c_1 h$ and $g leqslant c_2 h$ to $fracfg = fracc_1c_2$.



And the initial claim is false. Take, for example, $f(n) = h(n) = n^2$, $g(n) = n$.






share|cite|improve this answer









$endgroup$












  • $begingroup$
    Why can't I go to $ fracfg$
    $endgroup$
    – Leon1998
    Apr 26 at 11:01











  • $begingroup$
    Because why you would? Even with just numbers, no functions: $1 < 2$, $3 < 4$ but $frac13 neq frac24$. May be you wanted to write $fracfg leqslant fracc_1c_2$? It's still not true: you have $frac1g geqslant frac1c_2 h$, but you can multiply inequalities only with same direction.
    $endgroup$
    – mihaild
    Apr 26 at 11:06







  • 1




    $begingroup$
    Ok thank you. Now I see my mistake:)
    $endgroup$
    – Leon1998
    Apr 26 at 11:34


















7












$begingroup$

Consider $f(n)=h(n)=1$ and $g(n)=1/n$.






share|cite|improve this answer









$endgroup$













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    2 Answers
    2






    active

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    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    12












    $begingroup$

    You can't go from $f leqslant c_1 h$ and $g leqslant c_2 h$ to $fracfg = fracc_1c_2$.



    And the initial claim is false. Take, for example, $f(n) = h(n) = n^2$, $g(n) = n$.






    share|cite|improve this answer









    $endgroup$












    • $begingroup$
      Why can't I go to $ fracfg$
      $endgroup$
      – Leon1998
      Apr 26 at 11:01











    • $begingroup$
      Because why you would? Even with just numbers, no functions: $1 < 2$, $3 < 4$ but $frac13 neq frac24$. May be you wanted to write $fracfg leqslant fracc_1c_2$? It's still not true: you have $frac1g geqslant frac1c_2 h$, but you can multiply inequalities only with same direction.
      $endgroup$
      – mihaild
      Apr 26 at 11:06







    • 1




      $begingroup$
      Ok thank you. Now I see my mistake:)
      $endgroup$
      – Leon1998
      Apr 26 at 11:34















    12












    $begingroup$

    You can't go from $f leqslant c_1 h$ and $g leqslant c_2 h$ to $fracfg = fracc_1c_2$.



    And the initial claim is false. Take, for example, $f(n) = h(n) = n^2$, $g(n) = n$.






    share|cite|improve this answer









    $endgroup$












    • $begingroup$
      Why can't I go to $ fracfg$
      $endgroup$
      – Leon1998
      Apr 26 at 11:01











    • $begingroup$
      Because why you would? Even with just numbers, no functions: $1 < 2$, $3 < 4$ but $frac13 neq frac24$. May be you wanted to write $fracfg leqslant fracc_1c_2$? It's still not true: you have $frac1g geqslant frac1c_2 h$, but you can multiply inequalities only with same direction.
      $endgroup$
      – mihaild
      Apr 26 at 11:06







    • 1




      $begingroup$
      Ok thank you. Now I see my mistake:)
      $endgroup$
      – Leon1998
      Apr 26 at 11:34













    12












    12








    12





    $begingroup$

    You can't go from $f leqslant c_1 h$ and $g leqslant c_2 h$ to $fracfg = fracc_1c_2$.



    And the initial claim is false. Take, for example, $f(n) = h(n) = n^2$, $g(n) = n$.






    share|cite|improve this answer









    $endgroup$



    You can't go from $f leqslant c_1 h$ and $g leqslant c_2 h$ to $fracfg = fracc_1c_2$.



    And the initial claim is false. Take, for example, $f(n) = h(n) = n^2$, $g(n) = n$.







    share|cite|improve this answer












    share|cite|improve this answer



    share|cite|improve this answer










    answered Apr 26 at 11:00









    mihaildmihaild

    2,144216




    2,144216











    • $begingroup$
      Why can't I go to $ fracfg$
      $endgroup$
      – Leon1998
      Apr 26 at 11:01











    • $begingroup$
      Because why you would? Even with just numbers, no functions: $1 < 2$, $3 < 4$ but $frac13 neq frac24$. May be you wanted to write $fracfg leqslant fracc_1c_2$? It's still not true: you have $frac1g geqslant frac1c_2 h$, but you can multiply inequalities only with same direction.
      $endgroup$
      – mihaild
      Apr 26 at 11:06







    • 1




      $begingroup$
      Ok thank you. Now I see my mistake:)
      $endgroup$
      – Leon1998
      Apr 26 at 11:34
















    • $begingroup$
      Why can't I go to $ fracfg$
      $endgroup$
      – Leon1998
      Apr 26 at 11:01











    • $begingroup$
      Because why you would? Even with just numbers, no functions: $1 < 2$, $3 < 4$ but $frac13 neq frac24$. May be you wanted to write $fracfg leqslant fracc_1c_2$? It's still not true: you have $frac1g geqslant frac1c_2 h$, but you can multiply inequalities only with same direction.
      $endgroup$
      – mihaild
      Apr 26 at 11:06







    • 1




      $begingroup$
      Ok thank you. Now I see my mistake:)
      $endgroup$
      – Leon1998
      Apr 26 at 11:34















    $begingroup$
    Why can't I go to $ fracfg$
    $endgroup$
    – Leon1998
    Apr 26 at 11:01





    $begingroup$
    Why can't I go to $ fracfg$
    $endgroup$
    – Leon1998
    Apr 26 at 11:01













    $begingroup$
    Because why you would? Even with just numbers, no functions: $1 < 2$, $3 < 4$ but $frac13 neq frac24$. May be you wanted to write $fracfg leqslant fracc_1c_2$? It's still not true: you have $frac1g geqslant frac1c_2 h$, but you can multiply inequalities only with same direction.
    $endgroup$
    – mihaild
    Apr 26 at 11:06





    $begingroup$
    Because why you would? Even with just numbers, no functions: $1 < 2$, $3 < 4$ but $frac13 neq frac24$. May be you wanted to write $fracfg leqslant fracc_1c_2$? It's still not true: you have $frac1g geqslant frac1c_2 h$, but you can multiply inequalities only with same direction.
    $endgroup$
    – mihaild
    Apr 26 at 11:06





    1




    1




    $begingroup$
    Ok thank you. Now I see my mistake:)
    $endgroup$
    – Leon1998
    Apr 26 at 11:34




    $begingroup$
    Ok thank you. Now I see my mistake:)
    $endgroup$
    – Leon1998
    Apr 26 at 11:34











    7












    $begingroup$

    Consider $f(n)=h(n)=1$ and $g(n)=1/n$.






    share|cite|improve this answer









    $endgroup$

















      7












      $begingroup$

      Consider $f(n)=h(n)=1$ and $g(n)=1/n$.






      share|cite|improve this answer









      $endgroup$















        7












        7








        7





        $begingroup$

        Consider $f(n)=h(n)=1$ and $g(n)=1/n$.






        share|cite|improve this answer









        $endgroup$



        Consider $f(n)=h(n)=1$ and $g(n)=1/n$.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Apr 26 at 11:02









        FredFred

        48.8k11849




        48.8k11849



























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