typo in svm
This commit is contained in:
@@ -174,7 +174,7 @@ MathJax.Hub.Config({
|
||||
<center>[2] <b>Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University</b></center>
|
||||
<br>
|
||||
<p>
|
||||
<center><h4>Nov 18, 2019</h4></center> <!-- date -->
|
||||
<center><h4>Nov 22, 2019</h4></center> <!-- date -->
|
||||
<br>
|
||||
<p>
|
||||
|
||||
|
||||
@@ -166,7 +166,7 @@ $$
|
||||
<p>
|
||||
With our new basis, the equations we solved earlier are basically the same, that is we have now (without the slack option for simplicity)
|
||||
$$
|
||||
{\cal L}=\sum_i\lambda_i-\frac{1}{2}\sum_{ij}^n\lambda_i\lambda_jy_iy_j\boldsymbol{x}_i^T\boldsymbol{z}_j,
|
||||
{\cal L}=\sum_i\lambda_i-\frac{1}{2}\sum_{ij}^n\lambda_i\lambda_jy_iy_j\boldsymbol{z}_i^T\boldsymbol{z}_j,
|
||||
$$
|
||||
|
||||
subject to the constraints \( \lambda_i\geq 0 \), \( \sum_i\lambda_iy_i=0 \), and for the support vectors
|
||||
@@ -189,7 +189,10 @@ $$
|
||||
We note that this is nothing but the dot product of the two original
|
||||
vectors \( (\boldsymbol{x}_i^T\boldsymbol{x}_j)^2 \). Instead of thus computing the
|
||||
product in the Lagrangian of \( \boldsymbol{z}_i^T\boldsymbol{z}_j \) we simply compute
|
||||
the dot product \( (\boldsymbol{x}_i^T\boldsymbol{x}_j)^2 \). This leads to the so-called
|
||||
the dot product \( (\boldsymbol{x}_i^T\boldsymbol{x}_j)^2 \).
|
||||
|
||||
<p>
|
||||
This leads to the so-called
|
||||
kernel trick and the result leads to the same as if we went through
|
||||
the trouble of performing the transformation
|
||||
\( (\phi(\boldsymbol{x}_i)^T\phi(\boldsymbol{x}_j) \) during the SVM calculations.
|
||||
|
||||
@@ -170,18 +170,25 @@ There are several popular kernels being used. These are
|
||||
and many other ones.
|
||||
|
||||
<p>
|
||||
An important theorem for us is <a href="https://en.wikipedia.org/wiki/Mercer%27s_theorem" target="_self">Mercer's theorem</a>.
|
||||
The theorem states that if a kernel function \( K \) is symmetric, continuous and leads to a positive semi-definite matrix \( \boldsymbol{P} \) then
|
||||
there exists a function \( \phi \) that maps \( \boldsymbol{x}_i \) and \( \boldsymbol{x}_j \) into another space
|
||||
(possibly with much higher dimensions) such that
|
||||
An important theorem for us is <a href="https://en.wikipedia.org/wiki/Mercer%27s_theorem" target="_self">Mercer's
|
||||
theorem</a>. The
|
||||
theorem states that if a kernel function \( K \) is symmetric, continuous
|
||||
and leads to a positive semi-definite matrix \( \boldsymbol{P} \) then there
|
||||
exists a function \( \phi \) that maps \( \boldsymbol{x}_i \) and \( \boldsymbol{x}_j \) into
|
||||
another space (possibly with much higher dimensions) such that
|
||||
|
||||
$$
|
||||
K(\boldsymbol{x}_i,\boldsymbol{x}_j)=\phi(\boldsymbol{x}_i)^T\phi(\boldsymbol{x}_j).
|
||||
$$
|
||||
|
||||
<p>
|
||||
So you can use \( K \) as a kernel since you know \( \phi \) exists, even if
|
||||
you don’t know what \( \phi \) is.
|
||||
Note that some frequently used kernels (such as the Sigmoid kernel) don’t respect all of Mercer’s conditions, yet they generally work
|
||||
well in practice.
|
||||
you don’t know what \( \phi \) is.
|
||||
|
||||
<p>
|
||||
Note that some frequently used kernels (such as the Sigmoid kernel)
|
||||
don’t respect all of Mercer’s conditions, yet they generally work well
|
||||
in practice.
|
||||
|
||||
<p>
|
||||
<p>
|
||||
|
||||
@@ -174,7 +174,7 @@ MathJax.Hub.Config({
|
||||
<center>[2] <b>Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University</b></center>
|
||||
<br>
|
||||
<p>
|
||||
<center><h4>Nov 18, 2019</h4></center> <!-- date -->
|
||||
<center><h4>Nov 22, 2019</h4></center> <!-- date -->
|
||||
<br>
|
||||
<p>
|
||||
|
||||
|
||||
@@ -148,7 +148,7 @@ MathJax.Hub.Config({
|
||||
<center>[2] <b>Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University</b></center>
|
||||
<br>
|
||||
<p> <br>
|
||||
<center><h4>Nov 18, 2019</h4></center> <!-- date -->
|
||||
<center><h4>Nov 22, 2019</h4></center> <!-- date -->
|
||||
<br>
|
||||
<p>
|
||||
|
||||
@@ -988,7 +988,7 @@ $$
|
||||
With our new basis, the equations we solved earlier are basically the same, that is we have now (without the slack option for simplicity)
|
||||
<p> <br>
|
||||
$$
|
||||
{\cal L}=\sum_i\lambda_i-\frac{1}{2}\sum_{ij}^n\lambda_i\lambda_jy_iy_j\boldsymbol{x}_i^T\boldsymbol{z}_j,
|
||||
{\cal L}=\sum_i\lambda_i-\frac{1}{2}\sum_{ij}^n\lambda_i\lambda_jy_iy_j\boldsymbol{z}_i^T\boldsymbol{z}_j,
|
||||
$$
|
||||
<p> <br>
|
||||
|
||||
@@ -1018,7 +1018,10 @@ $$
|
||||
We note that this is nothing but the dot product of the two original
|
||||
vectors \( (\boldsymbol{x}_i^T\boldsymbol{x}_j)^2 \). Instead of thus computing the
|
||||
product in the Lagrangian of \( \boldsymbol{z}_i^T\boldsymbol{z}_j \) we simply compute
|
||||
the dot product \( (\boldsymbol{x}_i^T\boldsymbol{x}_j)^2 \). This leads to the so-called
|
||||
the dot product \( (\boldsymbol{x}_i^T\boldsymbol{x}_j)^2 \).
|
||||
|
||||
<p>
|
||||
This leads to the so-called
|
||||
kernel trick and the result leads to the same as if we went through
|
||||
the trouble of performing the transformation
|
||||
\( (\phi(\boldsymbol{x}_i)^T\phi(\boldsymbol{x}_j) \) during the SVM calculations.
|
||||
@@ -1084,20 +1087,27 @@ There are several popular kernels being used. These are
|
||||
and many other ones.
|
||||
|
||||
<p>
|
||||
An important theorem for us is <a href="https://en.wikipedia.org/wiki/Mercer%27s_theorem" target="_blank">Mercer's theorem</a>.
|
||||
The theorem states that if a kernel function \( K \) is symmetric, continuous and leads to a positive semi-definite matrix \( \boldsymbol{P} \) then
|
||||
there exists a function \( \phi \) that maps \( \boldsymbol{x}_i \) and \( \boldsymbol{x}_j \) into another space
|
||||
(possibly with much higher dimensions) such that
|
||||
An important theorem for us is <a href="https://en.wikipedia.org/wiki/Mercer%27s_theorem" target="_blank">Mercer's
|
||||
theorem</a>. The
|
||||
theorem states that if a kernel function \( K \) is symmetric, continuous
|
||||
and leads to a positive semi-definite matrix \( \boldsymbol{P} \) then there
|
||||
exists a function \( \phi \) that maps \( \boldsymbol{x}_i \) and \( \boldsymbol{x}_j \) into
|
||||
another space (possibly with much higher dimensions) such that
|
||||
|
||||
<p> <br>
|
||||
$$
|
||||
K(\boldsymbol{x}_i,\boldsymbol{x}_j)=\phi(\boldsymbol{x}_i)^T\phi(\boldsymbol{x}_j).
|
||||
$$
|
||||
<p> <br>
|
||||
|
||||
<p>
|
||||
So you can use \( K \) as a kernel since you know \( \phi \) exists, even if
|
||||
you don’t know what \( \phi \) is.
|
||||
Note that some frequently used kernels (such as the Sigmoid kernel) don’t respect all of Mercer’s conditions, yet they generally work
|
||||
well in practice.
|
||||
you don’t know what \( \phi \) is.
|
||||
|
||||
<p>
|
||||
Note that some frequently used kernels (such as the Sigmoid kernel)
|
||||
don’t respect all of Mercer’s conditions, yet they generally work well
|
||||
in practice.
|
||||
</section>
|
||||
|
||||
|
||||
|
||||
@@ -110,7 +110,7 @@ MathJax.Hub.Config({
|
||||
<center>[2] <b>Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University</b></center>
|
||||
<br>
|
||||
<p>
|
||||
<center><h4>Nov 18, 2019</h4></center> <!-- date -->
|
||||
<center><h4>Nov 22, 2019</h4></center> <!-- date -->
|
||||
<br>
|
||||
<p>
|
||||
<!-- !split --><br><br><br><br><br><br><br><br><br><br>
|
||||
@@ -831,7 +831,7 @@ $$
|
||||
<p>
|
||||
With our new basis, the equations we solved earlier are basically the same, that is we have now (without the slack option for simplicity)
|
||||
$$
|
||||
{\cal L}=\sum_i\lambda_i-\frac{1}{2}\sum_{ij}^n\lambda_i\lambda_jy_iy_j\boldsymbol{x}_i^T\boldsymbol{z}_j,
|
||||
{\cal L}=\sum_i\lambda_i-\frac{1}{2}\sum_{ij}^n\lambda_i\lambda_jy_iy_j\boldsymbol{z}_i^T\boldsymbol{z}_j,
|
||||
$$
|
||||
|
||||
subject to the constraints \( \lambda_i\geq 0 \), \( \sum_i\lambda_iy_i=0 \), and for the support vectors
|
||||
@@ -854,7 +854,10 @@ $$
|
||||
We note that this is nothing but the dot product of the two original
|
||||
vectors \( (\boldsymbol{x}_i^T\boldsymbol{x}_j)^2 \). Instead of thus computing the
|
||||
product in the Lagrangian of \( \boldsymbol{z}_i^T\boldsymbol{z}_j \) we simply compute
|
||||
the dot product \( (\boldsymbol{x}_i^T\boldsymbol{x}_j)^2 \). This leads to the so-called
|
||||
the dot product \( (\boldsymbol{x}_i^T\boldsymbol{x}_j)^2 \).
|
||||
|
||||
<p>
|
||||
This leads to the so-called
|
||||
kernel trick and the result leads to the same as if we went through
|
||||
the trouble of performing the transformation
|
||||
\( (\phi(\boldsymbol{x}_i)^T\phi(\boldsymbol{x}_j) \) during the SVM calculations.
|
||||
@@ -913,18 +916,25 @@ There are several popular kernels being used. These are
|
||||
and many other ones.
|
||||
|
||||
<p>
|
||||
An important theorem for us is <a href="https://en.wikipedia.org/wiki/Mercer%27s_theorem" target="_blank">Mercer's theorem</a>.
|
||||
The theorem states that if a kernel function \( K \) is symmetric, continuous and leads to a positive semi-definite matrix \( \boldsymbol{P} \) then
|
||||
there exists a function \( \phi \) that maps \( \boldsymbol{x}_i \) and \( \boldsymbol{x}_j \) into another space
|
||||
(possibly with much higher dimensions) such that
|
||||
An important theorem for us is <a href="https://en.wikipedia.org/wiki/Mercer%27s_theorem" target="_blank">Mercer's
|
||||
theorem</a>. The
|
||||
theorem states that if a kernel function \( K \) is symmetric, continuous
|
||||
and leads to a positive semi-definite matrix \( \boldsymbol{P} \) then there
|
||||
exists a function \( \phi \) that maps \( \boldsymbol{x}_i \) and \( \boldsymbol{x}_j \) into
|
||||
another space (possibly with much higher dimensions) such that
|
||||
|
||||
$$
|
||||
K(\boldsymbol{x}_i,\boldsymbol{x}_j)=\phi(\boldsymbol{x}_i)^T\phi(\boldsymbol{x}_j).
|
||||
$$
|
||||
|
||||
<p>
|
||||
So you can use \( K \) as a kernel since you know \( \phi \) exists, even if
|
||||
you don’t know what \( \phi \) is.
|
||||
Note that some frequently used kernels (such as the Sigmoid kernel) don’t respect all of Mercer’s conditions, yet they generally work
|
||||
well in practice.
|
||||
you don’t know what \( \phi \) is.
|
||||
|
||||
<p>
|
||||
Note that some frequently used kernels (such as the Sigmoid kernel)
|
||||
don’t respect all of Mercer’s conditions, yet they generally work well
|
||||
in practice.
|
||||
|
||||
<p>
|
||||
<!-- !split --><br><br><br><br><br><br><br><br><br><br>
|
||||
|
||||
+20
-10
@@ -115,7 +115,7 @@ MathJax.Hub.Config({
|
||||
<center>[2] <b>Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University</b></center>
|
||||
<br>
|
||||
<p>
|
||||
<center><h4>Nov 18, 2019</h4></center> <!-- date -->
|
||||
<center><h4>Nov 22, 2019</h4></center> <!-- date -->
|
||||
<br>
|
||||
<p>
|
||||
<!-- !split --><br><br><br><br><br><br><br><br><br><br>
|
||||
@@ -836,7 +836,7 @@ $$
|
||||
<p>
|
||||
With our new basis, the equations we solved earlier are basically the same, that is we have now (without the slack option for simplicity)
|
||||
$$
|
||||
{\cal L}=\sum_i\lambda_i-\frac{1}{2}\sum_{ij}^n\lambda_i\lambda_jy_iy_j\boldsymbol{x}_i^T\boldsymbol{z}_j,
|
||||
{\cal L}=\sum_i\lambda_i-\frac{1}{2}\sum_{ij}^n\lambda_i\lambda_jy_iy_j\boldsymbol{z}_i^T\boldsymbol{z}_j,
|
||||
$$
|
||||
|
||||
subject to the constraints \( \lambda_i\geq 0 \), \( \sum_i\lambda_iy_i=0 \), and for the support vectors
|
||||
@@ -859,7 +859,10 @@ $$
|
||||
We note that this is nothing but the dot product of the two original
|
||||
vectors \( (\boldsymbol{x}_i^T\boldsymbol{x}_j)^2 \). Instead of thus computing the
|
||||
product in the Lagrangian of \( \boldsymbol{z}_i^T\boldsymbol{z}_j \) we simply compute
|
||||
the dot product \( (\boldsymbol{x}_i^T\boldsymbol{x}_j)^2 \). This leads to the so-called
|
||||
the dot product \( (\boldsymbol{x}_i^T\boldsymbol{x}_j)^2 \).
|
||||
|
||||
<p>
|
||||
This leads to the so-called
|
||||
kernel trick and the result leads to the same as if we went through
|
||||
the trouble of performing the transformation
|
||||
\( (\phi(\boldsymbol{x}_i)^T\phi(\boldsymbol{x}_j) \) during the SVM calculations.
|
||||
@@ -918,18 +921,25 @@ There are several popular kernels being used. These are
|
||||
and many other ones.
|
||||
|
||||
<p>
|
||||
An important theorem for us is <a href="https://en.wikipedia.org/wiki/Mercer%27s_theorem" target="_blank">Mercer's theorem</a>.
|
||||
The theorem states that if a kernel function \( K \) is symmetric, continuous and leads to a positive semi-definite matrix \( \boldsymbol{P} \) then
|
||||
there exists a function \( \phi \) that maps \( \boldsymbol{x}_i \) and \( \boldsymbol{x}_j \) into another space
|
||||
(possibly with much higher dimensions) such that
|
||||
An important theorem for us is <a href="https://en.wikipedia.org/wiki/Mercer%27s_theorem" target="_blank">Mercer's
|
||||
theorem</a>. The
|
||||
theorem states that if a kernel function \( K \) is symmetric, continuous
|
||||
and leads to a positive semi-definite matrix \( \boldsymbol{P} \) then there
|
||||
exists a function \( \phi \) that maps \( \boldsymbol{x}_i \) and \( \boldsymbol{x}_j \) into
|
||||
another space (possibly with much higher dimensions) such that
|
||||
|
||||
$$
|
||||
K(\boldsymbol{x}_i,\boldsymbol{x}_j)=\phi(\boldsymbol{x}_i)^T\phi(\boldsymbol{x}_j).
|
||||
$$
|
||||
|
||||
<p>
|
||||
So you can use \( K \) as a kernel since you know \( \phi \) exists, even if
|
||||
you don’t know what \( \phi \) is.
|
||||
Note that some frequently used kernels (such as the Sigmoid kernel) don’t respect all of Mercer’s conditions, yet they generally work
|
||||
well in practice.
|
||||
you don’t know what \( \phi \) is.
|
||||
|
||||
<p>
|
||||
Note that some frequently used kernels (such as the Sigmoid kernel)
|
||||
don’t respect all of Mercer’s conditions, yet they generally work well
|
||||
in practice.
|
||||
|
||||
<p>
|
||||
<!-- !split --><br><br><br><br><br><br><br><br><br><br>
|
||||
|
||||
Binary file not shown.
@@ -10,7 +10,7 @@
|
||||
"<!-- Author: --> \n",
|
||||
"**Morten Hjorth-Jensen**, Department of Physics, University of Oslo and Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University\n",
|
||||
"\n",
|
||||
"Date: **Nov 18, 2019**\n",
|
||||
"Date: **Nov 22, 2019**\n",
|
||||
"\n",
|
||||
"Copyright 1999-2019, Morten Hjorth-Jensen. Released under CC Attribution-NonCommercial 4.0 license\n",
|
||||
"\n",
|
||||
@@ -1267,7 +1267,7 @@
|
||||
"metadata": {},
|
||||
"source": [
|
||||
"$$\n",
|
||||
"{\\cal L}=\\sum_i\\lambda_i-\\frac{1}{2}\\sum_{ij}^n\\lambda_i\\lambda_jy_iy_j\\boldsymbol{x}_i^T\\boldsymbol{z}_j,\n",
|
||||
"{\\cal L}=\\sum_i\\lambda_i-\\frac{1}{2}\\sum_{ij}^n\\lambda_i\\lambda_jy_iy_j\\boldsymbol{z}_i^T\\boldsymbol{z}_j,\n",
|
||||
"$$"
|
||||
]
|
||||
},
|
||||
@@ -1327,7 +1327,10 @@
|
||||
"We note that this is nothing but the dot product of the two original\n",
|
||||
"vectors $(\\boldsymbol{x}_i^T\\boldsymbol{x}_j)^2$. Instead of thus computing the\n",
|
||||
"product in the Lagrangian of $\\boldsymbol{z}_i^T\\boldsymbol{z}_j$ we simply compute\n",
|
||||
"the dot product $(\\boldsymbol{x}_i^T\\boldsymbol{x}_j)^2$. This leads to the so-called\n",
|
||||
"the dot product $(\\boldsymbol{x}_i^T\\boldsymbol{x}_j)^2$.\n",
|
||||
"\n",
|
||||
"\n",
|
||||
"This leads to the so-called\n",
|
||||
"kernel trick and the result leads to the same as if we went through\n",
|
||||
"the trouble of performing the transformation\n",
|
||||
"$(\\phi(\\boldsymbol{x}_i)^T\\phi(\\boldsymbol{x}_j)$ during the SVM calculations.\n",
|
||||
@@ -1412,10 +1415,12 @@
|
||||
"\n",
|
||||
"and many other ones.\n",
|
||||
"\n",
|
||||
"An important theorem for us is [Mercer's theorem](https://en.wikipedia.org/wiki/Mercer%27s_theorem). \n",
|
||||
"The theorem states that if a kernel function $K$ is symmetric, continuous and leads to a positive semi-definite matrix $\\boldsymbol{P}$ then\n",
|
||||
"there exists a function $\\phi$ that maps $\\boldsymbol{x}_i$ and $\\boldsymbol{x}_j$ into another space\n",
|
||||
"(possibly with much higher dimensions) such that"
|
||||
"An important theorem for us is [Mercer's\n",
|
||||
"theorem](https://en.wikipedia.org/wiki/Mercer%27s_theorem). The\n",
|
||||
"theorem states that if a kernel function $K$ is symmetric, continuous\n",
|
||||
"and leads to a positive semi-definite matrix $\\boldsymbol{P}$ then there\n",
|
||||
"exists a function $\\phi$ that maps $\\boldsymbol{x}_i$ and $\\boldsymbol{x}_j$ into\n",
|
||||
"another space (possibly with much higher dimensions) such that"
|
||||
]
|
||||
},
|
||||
{
|
||||
@@ -1433,8 +1438,10 @@
|
||||
"source": [
|
||||
"So you can use $K$ as a kernel since you know $\\phi$ exists, even if\n",
|
||||
"you don’t know what $\\phi$ is. \n",
|
||||
"Note that some frequently used kernels (such as the Sigmoid kernel) don’t respect all of Mercer’s conditions, yet they generally work\n",
|
||||
"well in practice.\n",
|
||||
"\n",
|
||||
"Note that some frequently used kernels (such as the Sigmoid kernel)\n",
|
||||
"don’t respect all of Mercer’s conditions, yet they generally work well\n",
|
||||
"in practice.\n",
|
||||
"\n",
|
||||
"\n",
|
||||
"## The moons example"
|
||||
|
||||
Binary file not shown.
@@ -708,7 +708,7 @@ z = \phi(x_i) =\left(x_i^2, y_i^2, \sqrt{2}x_iy_i\right).
|
||||
With our new basis, the equations we solved earlier are basically the same, that is we have now (without the slack option for simplicity)
|
||||
!bt
|
||||
\[
|
||||
{\cal L}=\sum_i\lambda_i-\frac{1}{2}\sum_{ij}^n\lambda_i\lambda_jy_iy_j\bm{x}_i^T\bm{z}_j,
|
||||
{\cal L}=\sum_i\lambda_i-\frac{1}{2}\sum_{ij}^n\lambda_i\lambda_jy_iy_j\bm{z}_i^T\bm{z}_j,
|
||||
\]
|
||||
!et
|
||||
subject to the constraints $\lambda_i\geq 0$, $\sum_i\lambda_iy_i=0$, and for the support vectors
|
||||
@@ -734,7 +734,10 @@ K(\bm{x}_i,\bm{x}_j)=[x_i^2, y_i^2, \sqrt{2}x_iy_i]^T\begin{bmatrix} x_j^2 \\ y_
|
||||
We note that this is nothing but the dot product of the two original
|
||||
vectors $(\bm{x}_i^T\bm{x}_j)^2$. Instead of thus computing the
|
||||
product in the Lagrangian of $\bm{z}_i^T\bm{z}_j$ we simply compute
|
||||
the dot product $(\bm{x}_i^T\bm{x}_j)^2$. This leads to the so-called
|
||||
the dot product $(\bm{x}_i^T\bm{x}_j)^2$.
|
||||
|
||||
|
||||
This leads to the so-called
|
||||
kernel trick and the result leads to the same as if we went through
|
||||
the trouble of performing the transformation
|
||||
$(\phi(\bm{x}_i)^T\phi(\bm{x}_j)$ during the SVM calculations.
|
||||
@@ -785,19 +788,25 @@ o Gaussian Radial Basis Function: $K(\bm{x},\bm{y})=\exp{\left(-\gamma\vert\vert
|
||||
o Tanh: $K(\bm{x},\bm{y})=\tanh{(\bm{x}^T\bm{y}+\gamma)}$,
|
||||
and many other ones.
|
||||
|
||||
An important theorem for us is "Mercer's theorem":"https://en.wikipedia.org/wiki/Mercer%27s_theorem".
|
||||
The theorem states that if a kernel function $K$ is symmetric, continuous and leads to a positive semi-definite matrix $\bm{P}$ then
|
||||
there exists a function $\phi$ that maps $\bm{x}_i$ and $\bm{x}_j$ into another space
|
||||
(possibly with much higher dimensions) such that
|
||||
An important theorem for us is "Mercer's
|
||||
theorem":"https://en.wikipedia.org/wiki/Mercer%27s_theorem". The
|
||||
theorem states that if a kernel function $K$ is symmetric, continuous
|
||||
and leads to a positive semi-definite matrix $\bm{P}$ then there
|
||||
exists a function $\phi$ that maps $\bm{x}_i$ and $\bm{x}_j$ into
|
||||
another space (possibly with much higher dimensions) such that
|
||||
|
||||
!bt
|
||||
\[
|
||||
K(\bm{x}_i,\bm{x}_j)=\phi(\bm{x}_i)^T\phi(\bm{x}_j).
|
||||
\]
|
||||
!et
|
||||
|
||||
So you can use $K$ as a kernel since you know $\phi$ exists, even if
|
||||
you don’t know what $\phi$ is.
|
||||
Note that some frequently used kernels (such as the Sigmoid kernel) don’t respect all of Mercer’s conditions, yet they generally work
|
||||
well in practice.
|
||||
|
||||
Note that some frequently used kernels (such as the Sigmoid kernel)
|
||||
don’t respect all of Mercer’s conditions, yet they generally work well
|
||||
in practice.
|
||||
|
||||
|
||||
!split
|
||||
|
||||
Reference in New Issue
Block a user