Substitution in an Integral from log to inverse
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Considering equations (2) (8) and (9) below. Please, I am wondering what is the insight into how the substitution was made to get (9). I have exhausted much energy trying to figure this out.
Note that the (2) in red is what I think was substituted into (8) from my own understanding. Also, how the $log (1+v)$ was changed to $frac{1}{v+1}$ is not clear to me. Pardon this seemingly easy but deep question.

integration substitution
$endgroup$
add a comment |
$begingroup$
Considering equations (2) (8) and (9) below. Please, I am wondering what is the insight into how the substitution was made to get (9). I have exhausted much energy trying to figure this out.
Note that the (2) in red is what I think was substituted into (8) from my own understanding. Also, how the $log (1+v)$ was changed to $frac{1}{v+1}$ is not clear to me. Pardon this seemingly easy but deep question.

integration substitution
$endgroup$
$begingroup$
This is integration by parts.
$endgroup$
– Chris Custer
Dec 28 '18 at 3:21
add a comment |
$begingroup$
Considering equations (2) (8) and (9) below. Please, I am wondering what is the insight into how the substitution was made to get (9). I have exhausted much energy trying to figure this out.
Note that the (2) in red is what I think was substituted into (8) from my own understanding. Also, how the $log (1+v)$ was changed to $frac{1}{v+1}$ is not clear to me. Pardon this seemingly easy but deep question.

integration substitution
$endgroup$
Considering equations (2) (8) and (9) below. Please, I am wondering what is the insight into how the substitution was made to get (9). I have exhausted much energy trying to figure this out.
Note that the (2) in red is what I think was substituted into (8) from my own understanding. Also, how the $log (1+v)$ was changed to $frac{1}{v+1}$ is not clear to me. Pardon this seemingly easy but deep question.

integration substitution
integration substitution
edited Dec 28 '18 at 3:49
Abdulhameed
asked Dec 28 '18 at 3:10
AbdulhameedAbdulhameed
153115
153115
$begingroup$
This is integration by parts.
$endgroup$
– Chris Custer
Dec 28 '18 at 3:21
add a comment |
$begingroup$
This is integration by parts.
$endgroup$
– Chris Custer
Dec 28 '18 at 3:21
$begingroup$
This is integration by parts.
$endgroup$
– Chris Custer
Dec 28 '18 at 3:21
$begingroup$
This is integration by parts.
$endgroup$
– Chris Custer
Dec 28 '18 at 3:21
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
$$C_{D2D}=lambda_dfrac1Nint_0^inftylog_2(1+nu)p(nu)dnu\=lambda_dfrac1{Nln2}int_0^infty ln(1+nu)p(nu)dnu$$Integrating by parts, and letting $P(nu)=int_infty^nu p(t) dt$,
$$C_{D2D}=lambda_dfrac1{Nln2}left[ln(1+nu)P(nu)right]_0^infty-lambda_dfrac1{Nln2}int_0^infty frac1{1+nu}P(nu)dnu$$The boundary term vanishes, leaving $$C_{D2D}=-lambda_dfrac1{Nln2}int_0^infty frac1{1+nu}(-exp(-zeta_{dr}(lambda_d+gamma_{dc}lambda_c)))dnu$$
which is as required (though I am not too sure why the $ln 2$ is not included in the solution in the paper).
$endgroup$
2
$begingroup$
The missing $ln 2$ was also bothering me.
$endgroup$
– Randall
Dec 28 '18 at 3:44
1
$begingroup$
Thanks John for this followable answer
$endgroup$
– Abdulhameed
Dec 28 '18 at 3:45
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@John, please at your convenience, may I see how intermediate steps between the third and fourth lines (The integration by parts) was done and the rationale behind the boundary term vanishing. I think I got something mixed up in my own trial. Thanks.
$endgroup$
– Abdulhameed
Dec 28 '18 at 4:42
$begingroup$
@Abdulhameed For the integration by parts, use $$int f frac{dg}{dnu} dnu=fg-intfrac{df}{dnu}gdnu$$ with $f(nu)=ln (1+nu)$ and $frac{dg(nu)}{dnu}=p(nu)$. Then $g(nu)=P(nu)$ due to how I defined $P(nu)$ as the integral of $p(nu)$. Differentiating the log gives us the $frac1{1+nu}$ term.
$endgroup$
– John Doe
Dec 28 '18 at 4:54
$begingroup$
The boundary term is (corrected from before), given by $$begin{align}left[ln(1+nu)P(nu)right]_0^infty&=lim_{nutoinfty}(ln(1+nu)P(nu))-ln(1)P(0)\&=-lim_{nutoinfty}left(ln(1+nu)int_nu^infty p(x) dxright)\&=-lim_{nutoinfty}[{-p(nu)}(1+nu)(ln(1+nu))^2]\&=0end{align}$$ Provided $p(nu)$ is sufficiently rapidly decaying as $nutoinfty$ (which is a reasonable assumption to make, and assuming $|P(0)|<infty$, which is true since $p(nu)$ is a p.d.f, so the area under it between $0$ and $infty$ is finite.
$endgroup$
– John Doe
Dec 28 '18 at 5:04
|
show 2 more comments
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Integration by parts works as follows: $$int f'g=fg-int fg'$$.
That would explain the appearance of $$(log(1+nu))'=frac1{1+nu}$$.
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No. Notice there are two terms, one being an integral. The $fg$ term is zero, i guess.
$endgroup$
– Chris Custer
Dec 28 '18 at 3:47
add a comment |
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$begingroup$
$$C_{D2D}=lambda_dfrac1Nint_0^inftylog_2(1+nu)p(nu)dnu\=lambda_dfrac1{Nln2}int_0^infty ln(1+nu)p(nu)dnu$$Integrating by parts, and letting $P(nu)=int_infty^nu p(t) dt$,
$$C_{D2D}=lambda_dfrac1{Nln2}left[ln(1+nu)P(nu)right]_0^infty-lambda_dfrac1{Nln2}int_0^infty frac1{1+nu}P(nu)dnu$$The boundary term vanishes, leaving $$C_{D2D}=-lambda_dfrac1{Nln2}int_0^infty frac1{1+nu}(-exp(-zeta_{dr}(lambda_d+gamma_{dc}lambda_c)))dnu$$
which is as required (though I am not too sure why the $ln 2$ is not included in the solution in the paper).
$endgroup$
2
$begingroup$
The missing $ln 2$ was also bothering me.
$endgroup$
– Randall
Dec 28 '18 at 3:44
1
$begingroup$
Thanks John for this followable answer
$endgroup$
– Abdulhameed
Dec 28 '18 at 3:45
$begingroup$
@John, please at your convenience, may I see how intermediate steps between the third and fourth lines (The integration by parts) was done and the rationale behind the boundary term vanishing. I think I got something mixed up in my own trial. Thanks.
$endgroup$
– Abdulhameed
Dec 28 '18 at 4:42
$begingroup$
@Abdulhameed For the integration by parts, use $$int f frac{dg}{dnu} dnu=fg-intfrac{df}{dnu}gdnu$$ with $f(nu)=ln (1+nu)$ and $frac{dg(nu)}{dnu}=p(nu)$. Then $g(nu)=P(nu)$ due to how I defined $P(nu)$ as the integral of $p(nu)$. Differentiating the log gives us the $frac1{1+nu}$ term.
$endgroup$
– John Doe
Dec 28 '18 at 4:54
$begingroup$
The boundary term is (corrected from before), given by $$begin{align}left[ln(1+nu)P(nu)right]_0^infty&=lim_{nutoinfty}(ln(1+nu)P(nu))-ln(1)P(0)\&=-lim_{nutoinfty}left(ln(1+nu)int_nu^infty p(x) dxright)\&=-lim_{nutoinfty}[{-p(nu)}(1+nu)(ln(1+nu))^2]\&=0end{align}$$ Provided $p(nu)$ is sufficiently rapidly decaying as $nutoinfty$ (which is a reasonable assumption to make, and assuming $|P(0)|<infty$, which is true since $p(nu)$ is a p.d.f, so the area under it between $0$ and $infty$ is finite.
$endgroup$
– John Doe
Dec 28 '18 at 5:04
|
show 2 more comments
$begingroup$
$$C_{D2D}=lambda_dfrac1Nint_0^inftylog_2(1+nu)p(nu)dnu\=lambda_dfrac1{Nln2}int_0^infty ln(1+nu)p(nu)dnu$$Integrating by parts, and letting $P(nu)=int_infty^nu p(t) dt$,
$$C_{D2D}=lambda_dfrac1{Nln2}left[ln(1+nu)P(nu)right]_0^infty-lambda_dfrac1{Nln2}int_0^infty frac1{1+nu}P(nu)dnu$$The boundary term vanishes, leaving $$C_{D2D}=-lambda_dfrac1{Nln2}int_0^infty frac1{1+nu}(-exp(-zeta_{dr}(lambda_d+gamma_{dc}lambda_c)))dnu$$
which is as required (though I am not too sure why the $ln 2$ is not included in the solution in the paper).
$endgroup$
2
$begingroup$
The missing $ln 2$ was also bothering me.
$endgroup$
– Randall
Dec 28 '18 at 3:44
1
$begingroup$
Thanks John for this followable answer
$endgroup$
– Abdulhameed
Dec 28 '18 at 3:45
$begingroup$
@John, please at your convenience, may I see how intermediate steps between the third and fourth lines (The integration by parts) was done and the rationale behind the boundary term vanishing. I think I got something mixed up in my own trial. Thanks.
$endgroup$
– Abdulhameed
Dec 28 '18 at 4:42
$begingroup$
@Abdulhameed For the integration by parts, use $$int f frac{dg}{dnu} dnu=fg-intfrac{df}{dnu}gdnu$$ with $f(nu)=ln (1+nu)$ and $frac{dg(nu)}{dnu}=p(nu)$. Then $g(nu)=P(nu)$ due to how I defined $P(nu)$ as the integral of $p(nu)$. Differentiating the log gives us the $frac1{1+nu}$ term.
$endgroup$
– John Doe
Dec 28 '18 at 4:54
$begingroup$
The boundary term is (corrected from before), given by $$begin{align}left[ln(1+nu)P(nu)right]_0^infty&=lim_{nutoinfty}(ln(1+nu)P(nu))-ln(1)P(0)\&=-lim_{nutoinfty}left(ln(1+nu)int_nu^infty p(x) dxright)\&=-lim_{nutoinfty}[{-p(nu)}(1+nu)(ln(1+nu))^2]\&=0end{align}$$ Provided $p(nu)$ is sufficiently rapidly decaying as $nutoinfty$ (which is a reasonable assumption to make, and assuming $|P(0)|<infty$, which is true since $p(nu)$ is a p.d.f, so the area under it between $0$ and $infty$ is finite.
$endgroup$
– John Doe
Dec 28 '18 at 5:04
|
show 2 more comments
$begingroup$
$$C_{D2D}=lambda_dfrac1Nint_0^inftylog_2(1+nu)p(nu)dnu\=lambda_dfrac1{Nln2}int_0^infty ln(1+nu)p(nu)dnu$$Integrating by parts, and letting $P(nu)=int_infty^nu p(t) dt$,
$$C_{D2D}=lambda_dfrac1{Nln2}left[ln(1+nu)P(nu)right]_0^infty-lambda_dfrac1{Nln2}int_0^infty frac1{1+nu}P(nu)dnu$$The boundary term vanishes, leaving $$C_{D2D}=-lambda_dfrac1{Nln2}int_0^infty frac1{1+nu}(-exp(-zeta_{dr}(lambda_d+gamma_{dc}lambda_c)))dnu$$
which is as required (though I am not too sure why the $ln 2$ is not included in the solution in the paper).
$endgroup$
$$C_{D2D}=lambda_dfrac1Nint_0^inftylog_2(1+nu)p(nu)dnu\=lambda_dfrac1{Nln2}int_0^infty ln(1+nu)p(nu)dnu$$Integrating by parts, and letting $P(nu)=int_infty^nu p(t) dt$,
$$C_{D2D}=lambda_dfrac1{Nln2}left[ln(1+nu)P(nu)right]_0^infty-lambda_dfrac1{Nln2}int_0^infty frac1{1+nu}P(nu)dnu$$The boundary term vanishes, leaving $$C_{D2D}=-lambda_dfrac1{Nln2}int_0^infty frac1{1+nu}(-exp(-zeta_{dr}(lambda_d+gamma_{dc}lambda_c)))dnu$$
which is as required (though I am not too sure why the $ln 2$ is not included in the solution in the paper).
edited Dec 28 '18 at 4:55
answered Dec 28 '18 at 3:35
John DoeJohn Doe
11.2k11239
11.2k11239
2
$begingroup$
The missing $ln 2$ was also bothering me.
$endgroup$
– Randall
Dec 28 '18 at 3:44
1
$begingroup$
Thanks John for this followable answer
$endgroup$
– Abdulhameed
Dec 28 '18 at 3:45
$begingroup$
@John, please at your convenience, may I see how intermediate steps between the third and fourth lines (The integration by parts) was done and the rationale behind the boundary term vanishing. I think I got something mixed up in my own trial. Thanks.
$endgroup$
– Abdulhameed
Dec 28 '18 at 4:42
$begingroup$
@Abdulhameed For the integration by parts, use $$int f frac{dg}{dnu} dnu=fg-intfrac{df}{dnu}gdnu$$ with $f(nu)=ln (1+nu)$ and $frac{dg(nu)}{dnu}=p(nu)$. Then $g(nu)=P(nu)$ due to how I defined $P(nu)$ as the integral of $p(nu)$. Differentiating the log gives us the $frac1{1+nu}$ term.
$endgroup$
– John Doe
Dec 28 '18 at 4:54
$begingroup$
The boundary term is (corrected from before), given by $$begin{align}left[ln(1+nu)P(nu)right]_0^infty&=lim_{nutoinfty}(ln(1+nu)P(nu))-ln(1)P(0)\&=-lim_{nutoinfty}left(ln(1+nu)int_nu^infty p(x) dxright)\&=-lim_{nutoinfty}[{-p(nu)}(1+nu)(ln(1+nu))^2]\&=0end{align}$$ Provided $p(nu)$ is sufficiently rapidly decaying as $nutoinfty$ (which is a reasonable assumption to make, and assuming $|P(0)|<infty$, which is true since $p(nu)$ is a p.d.f, so the area under it between $0$ and $infty$ is finite.
$endgroup$
– John Doe
Dec 28 '18 at 5:04
|
show 2 more comments
2
$begingroup$
The missing $ln 2$ was also bothering me.
$endgroup$
– Randall
Dec 28 '18 at 3:44
1
$begingroup$
Thanks John for this followable answer
$endgroup$
– Abdulhameed
Dec 28 '18 at 3:45
$begingroup$
@John, please at your convenience, may I see how intermediate steps between the third and fourth lines (The integration by parts) was done and the rationale behind the boundary term vanishing. I think I got something mixed up in my own trial. Thanks.
$endgroup$
– Abdulhameed
Dec 28 '18 at 4:42
$begingroup$
@Abdulhameed For the integration by parts, use $$int f frac{dg}{dnu} dnu=fg-intfrac{df}{dnu}gdnu$$ with $f(nu)=ln (1+nu)$ and $frac{dg(nu)}{dnu}=p(nu)$. Then $g(nu)=P(nu)$ due to how I defined $P(nu)$ as the integral of $p(nu)$. Differentiating the log gives us the $frac1{1+nu}$ term.
$endgroup$
– John Doe
Dec 28 '18 at 4:54
$begingroup$
The boundary term is (corrected from before), given by $$begin{align}left[ln(1+nu)P(nu)right]_0^infty&=lim_{nutoinfty}(ln(1+nu)P(nu))-ln(1)P(0)\&=-lim_{nutoinfty}left(ln(1+nu)int_nu^infty p(x) dxright)\&=-lim_{nutoinfty}[{-p(nu)}(1+nu)(ln(1+nu))^2]\&=0end{align}$$ Provided $p(nu)$ is sufficiently rapidly decaying as $nutoinfty$ (which is a reasonable assumption to make, and assuming $|P(0)|<infty$, which is true since $p(nu)$ is a p.d.f, so the area under it between $0$ and $infty$ is finite.
$endgroup$
– John Doe
Dec 28 '18 at 5:04
2
2
$begingroup$
The missing $ln 2$ was also bothering me.
$endgroup$
– Randall
Dec 28 '18 at 3:44
$begingroup$
The missing $ln 2$ was also bothering me.
$endgroup$
– Randall
Dec 28 '18 at 3:44
1
1
$begingroup$
Thanks John for this followable answer
$endgroup$
– Abdulhameed
Dec 28 '18 at 3:45
$begingroup$
Thanks John for this followable answer
$endgroup$
– Abdulhameed
Dec 28 '18 at 3:45
$begingroup$
@John, please at your convenience, may I see how intermediate steps between the third and fourth lines (The integration by parts) was done and the rationale behind the boundary term vanishing. I think I got something mixed up in my own trial. Thanks.
$endgroup$
– Abdulhameed
Dec 28 '18 at 4:42
$begingroup$
@John, please at your convenience, may I see how intermediate steps between the third and fourth lines (The integration by parts) was done and the rationale behind the boundary term vanishing. I think I got something mixed up in my own trial. Thanks.
$endgroup$
– Abdulhameed
Dec 28 '18 at 4:42
$begingroup$
@Abdulhameed For the integration by parts, use $$int f frac{dg}{dnu} dnu=fg-intfrac{df}{dnu}gdnu$$ with $f(nu)=ln (1+nu)$ and $frac{dg(nu)}{dnu}=p(nu)$. Then $g(nu)=P(nu)$ due to how I defined $P(nu)$ as the integral of $p(nu)$. Differentiating the log gives us the $frac1{1+nu}$ term.
$endgroup$
– John Doe
Dec 28 '18 at 4:54
$begingroup$
@Abdulhameed For the integration by parts, use $$int f frac{dg}{dnu} dnu=fg-intfrac{df}{dnu}gdnu$$ with $f(nu)=ln (1+nu)$ and $frac{dg(nu)}{dnu}=p(nu)$. Then $g(nu)=P(nu)$ due to how I defined $P(nu)$ as the integral of $p(nu)$. Differentiating the log gives us the $frac1{1+nu}$ term.
$endgroup$
– John Doe
Dec 28 '18 at 4:54
$begingroup$
The boundary term is (corrected from before), given by $$begin{align}left[ln(1+nu)P(nu)right]_0^infty&=lim_{nutoinfty}(ln(1+nu)P(nu))-ln(1)P(0)\&=-lim_{nutoinfty}left(ln(1+nu)int_nu^infty p(x) dxright)\&=-lim_{nutoinfty}[{-p(nu)}(1+nu)(ln(1+nu))^2]\&=0end{align}$$ Provided $p(nu)$ is sufficiently rapidly decaying as $nutoinfty$ (which is a reasonable assumption to make, and assuming $|P(0)|<infty$, which is true since $p(nu)$ is a p.d.f, so the area under it between $0$ and $infty$ is finite.
$endgroup$
– John Doe
Dec 28 '18 at 5:04
$begingroup$
The boundary term is (corrected from before), given by $$begin{align}left[ln(1+nu)P(nu)right]_0^infty&=lim_{nutoinfty}(ln(1+nu)P(nu))-ln(1)P(0)\&=-lim_{nutoinfty}left(ln(1+nu)int_nu^infty p(x) dxright)\&=-lim_{nutoinfty}[{-p(nu)}(1+nu)(ln(1+nu))^2]\&=0end{align}$$ Provided $p(nu)$ is sufficiently rapidly decaying as $nutoinfty$ (which is a reasonable assumption to make, and assuming $|P(0)|<infty$, which is true since $p(nu)$ is a p.d.f, so the area under it between $0$ and $infty$ is finite.
$endgroup$
– John Doe
Dec 28 '18 at 5:04
|
show 2 more comments
$begingroup$
Integration by parts works as follows: $$int f'g=fg-int fg'$$.
That would explain the appearance of $$(log(1+nu))'=frac1{1+nu}$$.
$endgroup$
$begingroup$
No. Notice there are two terms, one being an integral. The $fg$ term is zero, i guess.
$endgroup$
– Chris Custer
Dec 28 '18 at 3:47
add a comment |
$begingroup$
Integration by parts works as follows: $$int f'g=fg-int fg'$$.
That would explain the appearance of $$(log(1+nu))'=frac1{1+nu}$$.
$endgroup$
$begingroup$
No. Notice there are two terms, one being an integral. The $fg$ term is zero, i guess.
$endgroup$
– Chris Custer
Dec 28 '18 at 3:47
add a comment |
$begingroup$
Integration by parts works as follows: $$int f'g=fg-int fg'$$.
That would explain the appearance of $$(log(1+nu))'=frac1{1+nu}$$.
$endgroup$
Integration by parts works as follows: $$int f'g=fg-int fg'$$.
That would explain the appearance of $$(log(1+nu))'=frac1{1+nu}$$.
edited Dec 28 '18 at 3:47
answered Dec 28 '18 at 3:36
Chris CusterChris Custer
14.2k3827
14.2k3827
$begingroup$
No. Notice there are two terms, one being an integral. The $fg$ term is zero, i guess.
$endgroup$
– Chris Custer
Dec 28 '18 at 3:47
add a comment |
$begingroup$
No. Notice there are two terms, one being an integral. The $fg$ term is zero, i guess.
$endgroup$
– Chris Custer
Dec 28 '18 at 3:47
$begingroup$
No. Notice there are two terms, one being an integral. The $fg$ term is zero, i guess.
$endgroup$
– Chris Custer
Dec 28 '18 at 3:47
$begingroup$
No. Notice there are two terms, one being an integral. The $fg$ term is zero, i guess.
$endgroup$
– Chris Custer
Dec 28 '18 at 3:47
add a comment |
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$begingroup$
This is integration by parts.
$endgroup$
– Chris Custer
Dec 28 '18 at 3:21