Proving uniform convergence of a sequence of functions.











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I was wondering how to prove or disprove the following sequence of functions is uniformly convergent



$$ f(n) = frac{nt}{nt+1}, n≥1, t:[0,1] to R$$



So far I have analyzed the limits at $t=0$ and $t=1$ and believe it to be point-wise convergent, but not uniformly convergent. However, I'm not sure how to prove this.



Also, how does the above sequence vary from



$$ f(n) = frac{nt}{n+t}, n≥1, t:[0,1] to R$$
in regards to uniform convergence?










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  • Maybe you mean $f(t)$ or $f_n(t)$, with $t in [0, 1]$ and $n in mathbb{N}$, right?
    – the_candyman
    6 hours ago















up vote
1
down vote

favorite












I was wondering how to prove or disprove the following sequence of functions is uniformly convergent



$$ f(n) = frac{nt}{nt+1}, n≥1, t:[0,1] to R$$



So far I have analyzed the limits at $t=0$ and $t=1$ and believe it to be point-wise convergent, but not uniformly convergent. However, I'm not sure how to prove this.



Also, how does the above sequence vary from



$$ f(n) = frac{nt}{n+t}, n≥1, t:[0,1] to R$$
in regards to uniform convergence?










share|cite|improve this question









New contributor




MathGirl25 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.




















  • Maybe you mean $f(t)$ or $f_n(t)$, with $t in [0, 1]$ and $n in mathbb{N}$, right?
    – the_candyman
    6 hours ago













up vote
1
down vote

favorite









up vote
1
down vote

favorite











I was wondering how to prove or disprove the following sequence of functions is uniformly convergent



$$ f(n) = frac{nt}{nt+1}, n≥1, t:[0,1] to R$$



So far I have analyzed the limits at $t=0$ and $t=1$ and believe it to be point-wise convergent, but not uniformly convergent. However, I'm not sure how to prove this.



Also, how does the above sequence vary from



$$ f(n) = frac{nt}{n+t}, n≥1, t:[0,1] to R$$
in regards to uniform convergence?










share|cite|improve this question









New contributor




MathGirl25 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











I was wondering how to prove or disprove the following sequence of functions is uniformly convergent



$$ f(n) = frac{nt}{nt+1}, n≥1, t:[0,1] to R$$



So far I have analyzed the limits at $t=0$ and $t=1$ and believe it to be point-wise convergent, but not uniformly convergent. However, I'm not sure how to prove this.



Also, how does the above sequence vary from



$$ f(n) = frac{nt}{n+t}, n≥1, t:[0,1] to R$$
in regards to uniform convergence?







sequences-and-series convergence proof-writing






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edited 4 hours ago





















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asked 6 hours ago









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  • Maybe you mean $f(t)$ or $f_n(t)$, with $t in [0, 1]$ and $n in mathbb{N}$, right?
    – the_candyman
    6 hours ago


















  • Maybe you mean $f(t)$ or $f_n(t)$, with $t in [0, 1]$ and $n in mathbb{N}$, right?
    – the_candyman
    6 hours ago
















Maybe you mean $f(t)$ or $f_n(t)$, with $t in [0, 1]$ and $n in mathbb{N}$, right?
– the_candyman
6 hours ago




Maybe you mean $f(t)$ or $f_n(t)$, with $t in [0, 1]$ and $n in mathbb{N}$, right?
– the_candyman
6 hours ago










3 Answers
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3
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Observe $$f_n(t)=frac{nt}{nt+1}=dfrac{t}{t+dfrac{1}{n}}tobegin{cases}0 , &t=0\1, &tneq0end{cases}$$






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    up vote
    2
    down vote













    For $t$ fixed in $(0,1]$,



    $$lim_{nto+infty}f_n(t)=1=f(t)$$



    $$lim_{nto+infty}f_n(0)=0=f(0)$$



    the pointwise limit $f$ is not continuous at $[0,1]$, the convergence is Not uniform since all $f_n$ are continuous at $[0,1]$.






    share|cite|improve this answer






























      up vote
      1
      down vote













      The sequence



      $$f_n(t) = frac{nt}{nt+1}$$



      converges (in a point-wise sense) to:



      $$f(t) = begin{cases}
      0 & text{if}~t=0\
      1 & text{if}~0<tleq 1
      end{cases}.$$



      To check uniform convergence, you need to evaluate $d_n(t) = |f_n(t) - f(t)|$:



      $$d_n(t) = begin{cases}
      0 & text{if}~t=0\
      displaystyle frac{1}{nt+1} & text{if}~0<tleq 1
      end{cases}.$$



      Notice that:



      $$sup_{t in [0,1]} d_n(t) = 1,$$



      which does not converge to $0$ as $n$ goes to infinity. Therefore, convergence is not uniform.






      share|cite|improve this answer





















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        3 Answers
        3






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        3 Answers
        3






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        active

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        up vote
        3
        down vote













        Observe $$f_n(t)=frac{nt}{nt+1}=dfrac{t}{t+dfrac{1}{n}}tobegin{cases}0 , &t=0\1, &tneq0end{cases}$$






        share|cite|improve this answer

























          up vote
          3
          down vote













          Observe $$f_n(t)=frac{nt}{nt+1}=dfrac{t}{t+dfrac{1}{n}}tobegin{cases}0 , &t=0\1, &tneq0end{cases}$$






          share|cite|improve this answer























            up vote
            3
            down vote










            up vote
            3
            down vote









            Observe $$f_n(t)=frac{nt}{nt+1}=dfrac{t}{t+dfrac{1}{n}}tobegin{cases}0 , &t=0\1, &tneq0end{cases}$$






            share|cite|improve this answer












            Observe $$f_n(t)=frac{nt}{nt+1}=dfrac{t}{t+dfrac{1}{n}}tobegin{cases}0 , &t=0\1, &tneq0end{cases}$$







            share|cite|improve this answer












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            share|cite|improve this answer










            answered 6 hours ago









            Yadati Kiran

            1,289417




            1,289417






















                up vote
                2
                down vote













                For $t$ fixed in $(0,1]$,



                $$lim_{nto+infty}f_n(t)=1=f(t)$$



                $$lim_{nto+infty}f_n(0)=0=f(0)$$



                the pointwise limit $f$ is not continuous at $[0,1]$, the convergence is Not uniform since all $f_n$ are continuous at $[0,1]$.






                share|cite|improve this answer



























                  up vote
                  2
                  down vote













                  For $t$ fixed in $(0,1]$,



                  $$lim_{nto+infty}f_n(t)=1=f(t)$$



                  $$lim_{nto+infty}f_n(0)=0=f(0)$$



                  the pointwise limit $f$ is not continuous at $[0,1]$, the convergence is Not uniform since all $f_n$ are continuous at $[0,1]$.






                  share|cite|improve this answer

























                    up vote
                    2
                    down vote










                    up vote
                    2
                    down vote









                    For $t$ fixed in $(0,1]$,



                    $$lim_{nto+infty}f_n(t)=1=f(t)$$



                    $$lim_{nto+infty}f_n(0)=0=f(0)$$



                    the pointwise limit $f$ is not continuous at $[0,1]$, the convergence is Not uniform since all $f_n$ are continuous at $[0,1]$.






                    share|cite|improve this answer














                    For $t$ fixed in $(0,1]$,



                    $$lim_{nto+infty}f_n(t)=1=f(t)$$



                    $$lim_{nto+infty}f_n(0)=0=f(0)$$



                    the pointwise limit $f$ is not continuous at $[0,1]$, the convergence is Not uniform since all $f_n$ are continuous at $[0,1]$.







                    share|cite|improve this answer














                    share|cite|improve this answer



                    share|cite|improve this answer








                    edited 5 hours ago

























                    answered 6 hours ago









                    hamam_Abdallah

                    37.5k21634




                    37.5k21634






















                        up vote
                        1
                        down vote













                        The sequence



                        $$f_n(t) = frac{nt}{nt+1}$$



                        converges (in a point-wise sense) to:



                        $$f(t) = begin{cases}
                        0 & text{if}~t=0\
                        1 & text{if}~0<tleq 1
                        end{cases}.$$



                        To check uniform convergence, you need to evaluate $d_n(t) = |f_n(t) - f(t)|$:



                        $$d_n(t) = begin{cases}
                        0 & text{if}~t=0\
                        displaystyle frac{1}{nt+1} & text{if}~0<tleq 1
                        end{cases}.$$



                        Notice that:



                        $$sup_{t in [0,1]} d_n(t) = 1,$$



                        which does not converge to $0$ as $n$ goes to infinity. Therefore, convergence is not uniform.






                        share|cite|improve this answer

























                          up vote
                          1
                          down vote













                          The sequence



                          $$f_n(t) = frac{nt}{nt+1}$$



                          converges (in a point-wise sense) to:



                          $$f(t) = begin{cases}
                          0 & text{if}~t=0\
                          1 & text{if}~0<tleq 1
                          end{cases}.$$



                          To check uniform convergence, you need to evaluate $d_n(t) = |f_n(t) - f(t)|$:



                          $$d_n(t) = begin{cases}
                          0 & text{if}~t=0\
                          displaystyle frac{1}{nt+1} & text{if}~0<tleq 1
                          end{cases}.$$



                          Notice that:



                          $$sup_{t in [0,1]} d_n(t) = 1,$$



                          which does not converge to $0$ as $n$ goes to infinity. Therefore, convergence is not uniform.






                          share|cite|improve this answer























                            up vote
                            1
                            down vote










                            up vote
                            1
                            down vote









                            The sequence



                            $$f_n(t) = frac{nt}{nt+1}$$



                            converges (in a point-wise sense) to:



                            $$f(t) = begin{cases}
                            0 & text{if}~t=0\
                            1 & text{if}~0<tleq 1
                            end{cases}.$$



                            To check uniform convergence, you need to evaluate $d_n(t) = |f_n(t) - f(t)|$:



                            $$d_n(t) = begin{cases}
                            0 & text{if}~t=0\
                            displaystyle frac{1}{nt+1} & text{if}~0<tleq 1
                            end{cases}.$$



                            Notice that:



                            $$sup_{t in [0,1]} d_n(t) = 1,$$



                            which does not converge to $0$ as $n$ goes to infinity. Therefore, convergence is not uniform.






                            share|cite|improve this answer












                            The sequence



                            $$f_n(t) = frac{nt}{nt+1}$$



                            converges (in a point-wise sense) to:



                            $$f(t) = begin{cases}
                            0 & text{if}~t=0\
                            1 & text{if}~0<tleq 1
                            end{cases}.$$



                            To check uniform convergence, you need to evaluate $d_n(t) = |f_n(t) - f(t)|$:



                            $$d_n(t) = begin{cases}
                            0 & text{if}~t=0\
                            displaystyle frac{1}{nt+1} & text{if}~0<tleq 1
                            end{cases}.$$



                            Notice that:



                            $$sup_{t in [0,1]} d_n(t) = 1,$$



                            which does not converge to $0$ as $n$ goes to infinity. Therefore, convergence is not uniform.







                            share|cite|improve this answer












                            share|cite|improve this answer



                            share|cite|improve this answer










                            answered 6 hours ago









                            the_candyman

                            8,69822044




                            8,69822044






















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