Find Fourier transform of $delta(e^{ipi t}-i)$
$begingroup$
Find Fourier transform of $delta(e^{ipi t}-i)$
I used distribution $langledelta(t),phi(t)rangle=phi(0)$ but it didn't work.
fourier-transform
$endgroup$
add a comment |
$begingroup$
Find Fourier transform of $delta(e^{ipi t}-i)$
I used distribution $langledelta(t),phi(t)rangle=phi(0)$ but it didn't work.
fourier-transform
$endgroup$
$begingroup$
do you mean inverse fourier transform maybe ?
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 19:58
$begingroup$
@AhmadBazzi i wrote wrong, it was edited
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 20:08
$begingroup$
i have left you a detailed answer .. please check below.
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 20:37
add a comment |
$begingroup$
Find Fourier transform of $delta(e^{ipi t}-i)$
I used distribution $langledelta(t),phi(t)rangle=phi(0)$ but it didn't work.
fourier-transform
$endgroup$
Find Fourier transform of $delta(e^{ipi t}-i)$
I used distribution $langledelta(t),phi(t)rangle=phi(0)$ but it didn't work.
fourier-transform
fourier-transform
edited Dec 18 '18 at 21:07
Thien Hoang Dang
asked Dec 18 '18 at 19:46
Thien Hoang DangThien Hoang Dang
64
64
$begingroup$
do you mean inverse fourier transform maybe ?
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 19:58
$begingroup$
@AhmadBazzi i wrote wrong, it was edited
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 20:08
$begingroup$
i have left you a detailed answer .. please check below.
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 20:37
add a comment |
$begingroup$
do you mean inverse fourier transform maybe ?
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 19:58
$begingroup$
@AhmadBazzi i wrote wrong, it was edited
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 20:08
$begingroup$
i have left you a detailed answer .. please check below.
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 20:37
$begingroup$
do you mean inverse fourier transform maybe ?
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 19:58
$begingroup$
do you mean inverse fourier transform maybe ?
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 19:58
$begingroup$
@AhmadBazzi i wrote wrong, it was edited
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 20:08
$begingroup$
@AhmadBazzi i wrote wrong, it was edited
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 20:08
$begingroup$
i have left you a detailed answer .. please check below.
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 20:37
$begingroup$
i have left you a detailed answer .. please check below.
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 20:37
add a comment |
1 Answer
1
active
oldest
votes
$begingroup$
Note: The OP was originally to find the inverse Fourier Transform of $delta(e^{ipi f}-i)$
Credits: Thanks @Skip for the comment below
Notice that the argument is zero only when $e^{i pi f} = i$, or in other words
begin{equation}
pi f = frac{pi}{2} + 2k pi qquad k in mathbb{Z}
end{equation}
hence for $f = frac{1}{2 } + 2k$ where $k in mathbb{Z}$, the Dirac function peaks at $1$, else it is $0$. This results in a "Dirac comb" or "train of impulses" as
begin{equation}
delta(e^{ipi f}-i) = sum_{k = -infty}^{infty} delta(f - f_k)
end{equation}
where $f_k = frac{1}{2 } + 2k$. Applying inverse Fourier transforms on both sides, we have
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = sum_{k = -infty}^{infty} mathcal{F}^{-1}delta(f - f_k) tag{1}
end{equation}
Using the Fourier transform table, we know that
begin{equation}
mathcal{F}(e^{j 2 pi f_0 t})
=
2 pi delta(f - f_0)
end{equation}
which means that
begin{equation}
mathcal{F}^{-1}(delta(f - f_0)) = frac{1}{2pi}e^{j 2 pi f_0 t}tag{2}
end{equation}
Using equation $(2)$ in $(1)$ we get
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = frac{1}{2pi}sum_{k = -infty}^{infty} e^{j 2 pi f_k t}
end{equation}
Replacing $f_k =frac{1}{2 } + 2k$, we get
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = frac{1}{2pi}sum_{k = -infty}^{infty} e^{j 2 pi (frac{1}{2 } + 2k) t}
= frac{1}{2pi}e^{jpi t}sum_{k = -infty}^{infty} e^{4 k pi t }
end{equation}
$endgroup$
1
$begingroup$
I believe you meant $pi f = pi/2 + 2pi k$.
$endgroup$
– Skip
Dec 18 '18 at 20:29
1
$begingroup$
yes you are right .. thanks for drawing my attention @Skip
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 20:30
$begingroup$
nice solution @AhmadBazzi, but i want to find Fourier transform of $delta(e^{ipi t}-1)$
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:10
$begingroup$
but you just edited right now @ThienHoangDang
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 21:11
$begingroup$
sorry for wrong please bro @AhmadBazzi
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:12
|
show 3 more comments
Your Answer
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1 Answer
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$begingroup$
Note: The OP was originally to find the inverse Fourier Transform of $delta(e^{ipi f}-i)$
Credits: Thanks @Skip for the comment below
Notice that the argument is zero only when $e^{i pi f} = i$, or in other words
begin{equation}
pi f = frac{pi}{2} + 2k pi qquad k in mathbb{Z}
end{equation}
hence for $f = frac{1}{2 } + 2k$ where $k in mathbb{Z}$, the Dirac function peaks at $1$, else it is $0$. This results in a "Dirac comb" or "train of impulses" as
begin{equation}
delta(e^{ipi f}-i) = sum_{k = -infty}^{infty} delta(f - f_k)
end{equation}
where $f_k = frac{1}{2 } + 2k$. Applying inverse Fourier transforms on both sides, we have
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = sum_{k = -infty}^{infty} mathcal{F}^{-1}delta(f - f_k) tag{1}
end{equation}
Using the Fourier transform table, we know that
begin{equation}
mathcal{F}(e^{j 2 pi f_0 t})
=
2 pi delta(f - f_0)
end{equation}
which means that
begin{equation}
mathcal{F}^{-1}(delta(f - f_0)) = frac{1}{2pi}e^{j 2 pi f_0 t}tag{2}
end{equation}
Using equation $(2)$ in $(1)$ we get
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = frac{1}{2pi}sum_{k = -infty}^{infty} e^{j 2 pi f_k t}
end{equation}
Replacing $f_k =frac{1}{2 } + 2k$, we get
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = frac{1}{2pi}sum_{k = -infty}^{infty} e^{j 2 pi (frac{1}{2 } + 2k) t}
= frac{1}{2pi}e^{jpi t}sum_{k = -infty}^{infty} e^{4 k pi t }
end{equation}
$endgroup$
1
$begingroup$
I believe you meant $pi f = pi/2 + 2pi k$.
$endgroup$
– Skip
Dec 18 '18 at 20:29
1
$begingroup$
yes you are right .. thanks for drawing my attention @Skip
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 20:30
$begingroup$
nice solution @AhmadBazzi, but i want to find Fourier transform of $delta(e^{ipi t}-1)$
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:10
$begingroup$
but you just edited right now @ThienHoangDang
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 21:11
$begingroup$
sorry for wrong please bro @AhmadBazzi
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:12
|
show 3 more comments
$begingroup$
Note: The OP was originally to find the inverse Fourier Transform of $delta(e^{ipi f}-i)$
Credits: Thanks @Skip for the comment below
Notice that the argument is zero only when $e^{i pi f} = i$, or in other words
begin{equation}
pi f = frac{pi}{2} + 2k pi qquad k in mathbb{Z}
end{equation}
hence for $f = frac{1}{2 } + 2k$ where $k in mathbb{Z}$, the Dirac function peaks at $1$, else it is $0$. This results in a "Dirac comb" or "train of impulses" as
begin{equation}
delta(e^{ipi f}-i) = sum_{k = -infty}^{infty} delta(f - f_k)
end{equation}
where $f_k = frac{1}{2 } + 2k$. Applying inverse Fourier transforms on both sides, we have
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = sum_{k = -infty}^{infty} mathcal{F}^{-1}delta(f - f_k) tag{1}
end{equation}
Using the Fourier transform table, we know that
begin{equation}
mathcal{F}(e^{j 2 pi f_0 t})
=
2 pi delta(f - f_0)
end{equation}
which means that
begin{equation}
mathcal{F}^{-1}(delta(f - f_0)) = frac{1}{2pi}e^{j 2 pi f_0 t}tag{2}
end{equation}
Using equation $(2)$ in $(1)$ we get
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = frac{1}{2pi}sum_{k = -infty}^{infty} e^{j 2 pi f_k t}
end{equation}
Replacing $f_k =frac{1}{2 } + 2k$, we get
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = frac{1}{2pi}sum_{k = -infty}^{infty} e^{j 2 pi (frac{1}{2 } + 2k) t}
= frac{1}{2pi}e^{jpi t}sum_{k = -infty}^{infty} e^{4 k pi t }
end{equation}
$endgroup$
1
$begingroup$
I believe you meant $pi f = pi/2 + 2pi k$.
$endgroup$
– Skip
Dec 18 '18 at 20:29
1
$begingroup$
yes you are right .. thanks for drawing my attention @Skip
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 20:30
$begingroup$
nice solution @AhmadBazzi, but i want to find Fourier transform of $delta(e^{ipi t}-1)$
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:10
$begingroup$
but you just edited right now @ThienHoangDang
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 21:11
$begingroup$
sorry for wrong please bro @AhmadBazzi
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:12
|
show 3 more comments
$begingroup$
Note: The OP was originally to find the inverse Fourier Transform of $delta(e^{ipi f}-i)$
Credits: Thanks @Skip for the comment below
Notice that the argument is zero only when $e^{i pi f} = i$, or in other words
begin{equation}
pi f = frac{pi}{2} + 2k pi qquad k in mathbb{Z}
end{equation}
hence for $f = frac{1}{2 } + 2k$ where $k in mathbb{Z}$, the Dirac function peaks at $1$, else it is $0$. This results in a "Dirac comb" or "train of impulses" as
begin{equation}
delta(e^{ipi f}-i) = sum_{k = -infty}^{infty} delta(f - f_k)
end{equation}
where $f_k = frac{1}{2 } + 2k$. Applying inverse Fourier transforms on both sides, we have
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = sum_{k = -infty}^{infty} mathcal{F}^{-1}delta(f - f_k) tag{1}
end{equation}
Using the Fourier transform table, we know that
begin{equation}
mathcal{F}(e^{j 2 pi f_0 t})
=
2 pi delta(f - f_0)
end{equation}
which means that
begin{equation}
mathcal{F}^{-1}(delta(f - f_0)) = frac{1}{2pi}e^{j 2 pi f_0 t}tag{2}
end{equation}
Using equation $(2)$ in $(1)$ we get
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = frac{1}{2pi}sum_{k = -infty}^{infty} e^{j 2 pi f_k t}
end{equation}
Replacing $f_k =frac{1}{2 } + 2k$, we get
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = frac{1}{2pi}sum_{k = -infty}^{infty} e^{j 2 pi (frac{1}{2 } + 2k) t}
= frac{1}{2pi}e^{jpi t}sum_{k = -infty}^{infty} e^{4 k pi t }
end{equation}
$endgroup$
Note: The OP was originally to find the inverse Fourier Transform of $delta(e^{ipi f}-i)$
Credits: Thanks @Skip for the comment below
Notice that the argument is zero only when $e^{i pi f} = i$, or in other words
begin{equation}
pi f = frac{pi}{2} + 2k pi qquad k in mathbb{Z}
end{equation}
hence for $f = frac{1}{2 } + 2k$ where $k in mathbb{Z}$, the Dirac function peaks at $1$, else it is $0$. This results in a "Dirac comb" or "train of impulses" as
begin{equation}
delta(e^{ipi f}-i) = sum_{k = -infty}^{infty} delta(f - f_k)
end{equation}
where $f_k = frac{1}{2 } + 2k$. Applying inverse Fourier transforms on both sides, we have
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = sum_{k = -infty}^{infty} mathcal{F}^{-1}delta(f - f_k) tag{1}
end{equation}
Using the Fourier transform table, we know that
begin{equation}
mathcal{F}(e^{j 2 pi f_0 t})
=
2 pi delta(f - f_0)
end{equation}
which means that
begin{equation}
mathcal{F}^{-1}(delta(f - f_0)) = frac{1}{2pi}e^{j 2 pi f_0 t}tag{2}
end{equation}
Using equation $(2)$ in $(1)$ we get
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = frac{1}{2pi}sum_{k = -infty}^{infty} e^{j 2 pi f_k t}
end{equation}
Replacing $f_k =frac{1}{2 } + 2k$, we get
begin{equation}
mathcal{F}^{-1}delta(e^{ipi f}-i) = frac{1}{2pi}sum_{k = -infty}^{infty} e^{j 2 pi (frac{1}{2 } + 2k) t}
= frac{1}{2pi}e^{jpi t}sum_{k = -infty}^{infty} e^{4 k pi t }
end{equation}
edited Dec 18 '18 at 21:13
answered Dec 18 '18 at 20:16
Ahmad BazziAhmad Bazzi
8,0012724
8,0012724
1
$begingroup$
I believe you meant $pi f = pi/2 + 2pi k$.
$endgroup$
– Skip
Dec 18 '18 at 20:29
1
$begingroup$
yes you are right .. thanks for drawing my attention @Skip
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 20:30
$begingroup$
nice solution @AhmadBazzi, but i want to find Fourier transform of $delta(e^{ipi t}-1)$
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:10
$begingroup$
but you just edited right now @ThienHoangDang
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 21:11
$begingroup$
sorry for wrong please bro @AhmadBazzi
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:12
|
show 3 more comments
1
$begingroup$
I believe you meant $pi f = pi/2 + 2pi k$.
$endgroup$
– Skip
Dec 18 '18 at 20:29
1
$begingroup$
yes you are right .. thanks for drawing my attention @Skip
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 20:30
$begingroup$
nice solution @AhmadBazzi, but i want to find Fourier transform of $delta(e^{ipi t}-1)$
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:10
$begingroup$
but you just edited right now @ThienHoangDang
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 21:11
$begingroup$
sorry for wrong please bro @AhmadBazzi
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:12
1
1
$begingroup$
I believe you meant $pi f = pi/2 + 2pi k$.
$endgroup$
– Skip
Dec 18 '18 at 20:29
$begingroup$
I believe you meant $pi f = pi/2 + 2pi k$.
$endgroup$
– Skip
Dec 18 '18 at 20:29
1
1
$begingroup$
yes you are right .. thanks for drawing my attention @Skip
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 20:30
$begingroup$
yes you are right .. thanks for drawing my attention @Skip
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 20:30
$begingroup$
nice solution @AhmadBazzi, but i want to find Fourier transform of $delta(e^{ipi t}-1)$
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:10
$begingroup$
nice solution @AhmadBazzi, but i want to find Fourier transform of $delta(e^{ipi t}-1)$
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:10
$begingroup$
but you just edited right now @ThienHoangDang
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 21:11
$begingroup$
but you just edited right now @ThienHoangDang
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 21:11
$begingroup$
sorry for wrong please bro @AhmadBazzi
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:12
$begingroup$
sorry for wrong please bro @AhmadBazzi
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 21:12
|
show 3 more comments
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$begingroup$
do you mean inverse fourier transform maybe ?
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 19:58
$begingroup$
@AhmadBazzi i wrote wrong, it was edited
$endgroup$
– Thien Hoang Dang
Dec 18 '18 at 20:08
$begingroup$
i have left you a detailed answer .. please check below.
$endgroup$
– Ahmad Bazzi
Dec 18 '18 at 20:37