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Problem at deriving Bachelier formula with interest rates


Why is the black-scholes model arbitrage free when σ>0?Square of arithmetic brownian motion processStochastic process and brownian motionpricing option with two stocksChange-of-measure: Dynamics of $log(S_t)$ with $S_t$ as numeraireBlack & Scholes with stochastic interest ratePricing caplet with Bachelier (normal dynamic) using forward measureQuestion about Stochastic Calculus,(change of measure)?Ultra Powerfull Vibrato Montecarlo for delta sensitivities of a not regular payoffEquivalence of Put Pricing Formulas






.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;








3












$begingroup$


In the Bachelier model, I have difficulties with a certain step. I want to figure out the distribution of $S_T$, which is the price process in the Bachelier model.



So far I could state that ($mathbbQ$ is the EMM):
begineqnarray
dS_t = r S_t dt + sigma W^mathbbQ_t labelSDE2
endeqnarray

and with that
begineqnarray
S_T = S_0 e^rT + intlimits_0^Tsigma e^r(T-s) dW^mathbbQ_s
endeqnarray

Now I have found a book that states that $S_T$ has distribution:
begineqnarray
S_T sim mathscr N left(S_0 e^rT, sqrtfracsigma^2-sigma^2e^-2rT2r right)
endeqnarray



I do not understand why this should be, maybe my skills in stochastic integration are not sufficient.



Thank you for taking your time!










share|improve this question











$endgroup$







  • 4




    $begingroup$
    This is a direct application of Ito's isometry: en.m.wikipedia.org/wiki/It%C3%B4_isometry it gives you the mean (= 0) and variance ($= int f^2(u)du$) of a Wiener integral $int f(u) dW(u)$.
    $endgroup$
    – byouness
    Jun 26 at 8:00


















3












$begingroup$


In the Bachelier model, I have difficulties with a certain step. I want to figure out the distribution of $S_T$, which is the price process in the Bachelier model.



So far I could state that ($mathbbQ$ is the EMM):
begineqnarray
dS_t = r S_t dt + sigma W^mathbbQ_t labelSDE2
endeqnarray

and with that
begineqnarray
S_T = S_0 e^rT + intlimits_0^Tsigma e^r(T-s) dW^mathbbQ_s
endeqnarray

Now I have found a book that states that $S_T$ has distribution:
begineqnarray
S_T sim mathscr N left(S_0 e^rT, sqrtfracsigma^2-sigma^2e^-2rT2r right)
endeqnarray



I do not understand why this should be, maybe my skills in stochastic integration are not sufficient.



Thank you for taking your time!










share|improve this question











$endgroup$







  • 4




    $begingroup$
    This is a direct application of Ito's isometry: en.m.wikipedia.org/wiki/It%C3%B4_isometry it gives you the mean (= 0) and variance ($= int f^2(u)du$) of a Wiener integral $int f(u) dW(u)$.
    $endgroup$
    – byouness
    Jun 26 at 8:00














3












3








3


1



$begingroup$


In the Bachelier model, I have difficulties with a certain step. I want to figure out the distribution of $S_T$, which is the price process in the Bachelier model.



So far I could state that ($mathbbQ$ is the EMM):
begineqnarray
dS_t = r S_t dt + sigma W^mathbbQ_t labelSDE2
endeqnarray

and with that
begineqnarray
S_T = S_0 e^rT + intlimits_0^Tsigma e^r(T-s) dW^mathbbQ_s
endeqnarray

Now I have found a book that states that $S_T$ has distribution:
begineqnarray
S_T sim mathscr N left(S_0 e^rT, sqrtfracsigma^2-sigma^2e^-2rT2r right)
endeqnarray



I do not understand why this should be, maybe my skills in stochastic integration are not sufficient.



Thank you for taking your time!










share|improve this question











$endgroup$




In the Bachelier model, I have difficulties with a certain step. I want to figure out the distribution of $S_T$, which is the price process in the Bachelier model.



So far I could state that ($mathbbQ$ is the EMM):
begineqnarray
dS_t = r S_t dt + sigma W^mathbbQ_t labelSDE2
endeqnarray

and with that
begineqnarray
S_T = S_0 e^rT + intlimits_0^Tsigma e^r(T-s) dW^mathbbQ_s
endeqnarray

Now I have found a book that states that $S_T$ has distribution:
begineqnarray
S_T sim mathscr N left(S_0 e^rT, sqrtfracsigma^2-sigma^2e^-2rT2r right)
endeqnarray



I do not understand why this should be, maybe my skills in stochastic integration are not sufficient.



Thank you for taking your time!







options stochastic-calculus pricing models






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Jun 26 at 7:48







cruiser0223

















asked Jun 26 at 7:43









cruiser0223cruiser0223

184 bronze badges




184 bronze badges







  • 4




    $begingroup$
    This is a direct application of Ito's isometry: en.m.wikipedia.org/wiki/It%C3%B4_isometry it gives you the mean (= 0) and variance ($= int f^2(u)du$) of a Wiener integral $int f(u) dW(u)$.
    $endgroup$
    – byouness
    Jun 26 at 8:00













  • 4




    $begingroup$
    This is a direct application of Ito's isometry: en.m.wikipedia.org/wiki/It%C3%B4_isometry it gives you the mean (= 0) and variance ($= int f^2(u)du$) of a Wiener integral $int f(u) dW(u)$.
    $endgroup$
    – byouness
    Jun 26 at 8:00








4




4




$begingroup$
This is a direct application of Ito's isometry: en.m.wikipedia.org/wiki/It%C3%B4_isometry it gives you the mean (= 0) and variance ($= int f^2(u)du$) of a Wiener integral $int f(u) dW(u)$.
$endgroup$
– byouness
Jun 26 at 8:00





$begingroup$
This is a direct application of Ito's isometry: en.m.wikipedia.org/wiki/It%C3%B4_isometry it gives you the mean (= 0) and variance ($= int f^2(u)du$) of a Wiener integral $int f(u) dW(u)$.
$endgroup$
– byouness
Jun 26 at 8:00











1 Answer
1






active

oldest

votes


















4












$begingroup$

As explained by @byouness, using Itô's Isometry, we get:
$$beginalign
V(S_T)&=V^mathbbQleft(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)
\[9pt]
&=E^mathbbQleft(left(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)^2right)-underbraceE^mathbbQleft(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)_=int_0^Tsigma e^r(T-s) E^mathbbQ(dW^mathbbQ_s)=0^2
\[-9pt]
&=E^mathbbQleft(int_0^Tsigma^2 e^2r(T-s) dsright)
endalign$$

The remaining integral is deterministic, thus:
$$V(S_T)=sigma^2left[-frace^2r(T-s)2rright]_s=0^s=T=sigma^2left(frace^2rT-12rright)$$
Note that your result is correct up to a minus sign. This is probably because the Bachelier dynamics for the stock price are also known as an Ornstein–Uhlenbeck process, which is normally defined with a minus sign in the drift, i.e.:
$$dS_t = colorred-r S_t dt + sigma W^mathbbQ_t$$
in which case the volatility is given by the expression in your original post.






share|improve this answer









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    1 Answer
    1






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    active

    oldest

    votes






    active

    oldest

    votes









    4












    $begingroup$

    As explained by @byouness, using Itô's Isometry, we get:
    $$beginalign
    V(S_T)&=V^mathbbQleft(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)
    \[9pt]
    &=E^mathbbQleft(left(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)^2right)-underbraceE^mathbbQleft(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)_=int_0^Tsigma e^r(T-s) E^mathbbQ(dW^mathbbQ_s)=0^2
    \[-9pt]
    &=E^mathbbQleft(int_0^Tsigma^2 e^2r(T-s) dsright)
    endalign$$

    The remaining integral is deterministic, thus:
    $$V(S_T)=sigma^2left[-frace^2r(T-s)2rright]_s=0^s=T=sigma^2left(frace^2rT-12rright)$$
    Note that your result is correct up to a minus sign. This is probably because the Bachelier dynamics for the stock price are also known as an Ornstein–Uhlenbeck process, which is normally defined with a minus sign in the drift, i.e.:
    $$dS_t = colorred-r S_t dt + sigma W^mathbbQ_t$$
    in which case the volatility is given by the expression in your original post.






    share|improve this answer









    $endgroup$

















      4












      $begingroup$

      As explained by @byouness, using Itô's Isometry, we get:
      $$beginalign
      V(S_T)&=V^mathbbQleft(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)
      \[9pt]
      &=E^mathbbQleft(left(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)^2right)-underbraceE^mathbbQleft(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)_=int_0^Tsigma e^r(T-s) E^mathbbQ(dW^mathbbQ_s)=0^2
      \[-9pt]
      &=E^mathbbQleft(int_0^Tsigma^2 e^2r(T-s) dsright)
      endalign$$

      The remaining integral is deterministic, thus:
      $$V(S_T)=sigma^2left[-frace^2r(T-s)2rright]_s=0^s=T=sigma^2left(frace^2rT-12rright)$$
      Note that your result is correct up to a minus sign. This is probably because the Bachelier dynamics for the stock price are also known as an Ornstein–Uhlenbeck process, which is normally defined with a minus sign in the drift, i.e.:
      $$dS_t = colorred-r S_t dt + sigma W^mathbbQ_t$$
      in which case the volatility is given by the expression in your original post.






      share|improve this answer









      $endgroup$















        4












        4








        4





        $begingroup$

        As explained by @byouness, using Itô's Isometry, we get:
        $$beginalign
        V(S_T)&=V^mathbbQleft(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)
        \[9pt]
        &=E^mathbbQleft(left(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)^2right)-underbraceE^mathbbQleft(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)_=int_0^Tsigma e^r(T-s) E^mathbbQ(dW^mathbbQ_s)=0^2
        \[-9pt]
        &=E^mathbbQleft(int_0^Tsigma^2 e^2r(T-s) dsright)
        endalign$$

        The remaining integral is deterministic, thus:
        $$V(S_T)=sigma^2left[-frace^2r(T-s)2rright]_s=0^s=T=sigma^2left(frace^2rT-12rright)$$
        Note that your result is correct up to a minus sign. This is probably because the Bachelier dynamics for the stock price are also known as an Ornstein–Uhlenbeck process, which is normally defined with a minus sign in the drift, i.e.:
        $$dS_t = colorred-r S_t dt + sigma W^mathbbQ_t$$
        in which case the volatility is given by the expression in your original post.






        share|improve this answer









        $endgroup$



        As explained by @byouness, using Itô's Isometry, we get:
        $$beginalign
        V(S_T)&=V^mathbbQleft(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)
        \[9pt]
        &=E^mathbbQleft(left(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)^2right)-underbraceE^mathbbQleft(int_0^Tsigma e^r(T-s) dW^mathbbQ_sright)_=int_0^Tsigma e^r(T-s) E^mathbbQ(dW^mathbbQ_s)=0^2
        \[-9pt]
        &=E^mathbbQleft(int_0^Tsigma^2 e^2r(T-s) dsright)
        endalign$$

        The remaining integral is deterministic, thus:
        $$V(S_T)=sigma^2left[-frace^2r(T-s)2rright]_s=0^s=T=sigma^2left(frace^2rT-12rright)$$
        Note that your result is correct up to a minus sign. This is probably because the Bachelier dynamics for the stock price are also known as an Ornstein–Uhlenbeck process, which is normally defined with a minus sign in the drift, i.e.:
        $$dS_t = colorred-r S_t dt + sigma W^mathbbQ_t$$
        in which case the volatility is given by the expression in your original post.







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Jun 26 at 9:11









        Daneel OlivawDaneel Olivaw

        3,3431 gold badge8 silver badges31 bronze badges




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