mirror of https://github.com/CGAL/cgal
Use \ccSum.
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@ -7,11 +7,11 @@ re-produces linear functions exactly. The interpolation of
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$\Phi(\mathbf{x})$ is given as the linear combination of the neighbors' function
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values weighted by the coordinates:
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\begin{displaymath}
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Z^0(\mathbf{x}) = \sum_i \lambda_i(\mathbf{x}) z_i.
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Z^0(\mathbf{x}) = \ccSum{i}{}{ \lambda_i(\mathbf{x}) z_i}.
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\end{displaymath}
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Indeed, if $z_i=a + \mathbf{b}^t \mathbf{p_i}$ for all natural
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neighbors of $\mathbf{x}$, we have
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\[ Z^0(\mathbf{x}) = \sum_i \lambda_i(\mathbf{x}) (a + \mathbf{b}^t\mathbf{p_i}) = a+\mathbf{b}^t \mathbf{x}\]
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\[ Z^0(\mathbf{x}) = \ccSum{i}{}{ \lambda_i(\mathbf{x}) (a + \mathbf{b}^t\mathbf{p_i})} = a+\mathbf{b}^t \mathbf{x}\]
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by the barycentric coordinate property. The first example in
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Subsection~\ref{subsec:interpol_examples} shows how the function is
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called.
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@ -31,20 +31,20 @@ Sibson's $Z^1$ interpolant is a combination of the linear interpolant
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$Z^0$ and an interpolant $\xi$ which is the weighted sum of the first
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degree functions
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$$\xi_i(\mathbf{x}) = z_i
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+\mathbf{g_i}^t(\mathbf{x}-\mathbf{p_i}),\qquad \xi(\mathbf{x})= \frac{\sum_i \frac{\lambda_i(\mathbf{x})}
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{\|\mathbf{x}-\mathbf{p_i}\|}\xi_i(\mathbf{x}) }{\sum_i
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\frac{\lambda_i(\mathbf{x})}{\|\mathbf{x}-\mathbf{p_i}\|}}.$$
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+\mathbf{g_i}^t(\mathbf{x}-\mathbf{p_i}),\qquad \xi(\mathbf{x})= \frac{\ccSum{i}{}{ \frac{\lambda_i(\mathbf{x})}
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{\|\mathbf{x}-\mathbf{p_i}\|}\xi_i(\mathbf{x}) } }{\ccSum{i}{}{
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\frac{\lambda_i(\mathbf{x})}{\|\mathbf{x}-\mathbf{p_i}\|}}}.$$
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Sibson observed that the combination of $Z^0$ and $\xi$ reconstructs exactly
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a spherical quadric if they are mixed as follows:
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$$
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Z^1(\mathbf{x}) = \frac{\alpha(\mathbf{x}) Z^0(\mathbf{x}) +
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\beta(\mathbf{x}) \xi(\mathbf{x})}{\alpha(\mathbf{x}) +
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\beta(\mathbf{x})} \textrm{ where } \alpha(\mathbf{x}) =
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\frac{\sum_i \lambda_i(\mathbf{x}) \frac{\|\mathbf{x} -
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\mathbf{p_i}\|^2}{f(\|\mathbf{x} - \mathbf{p_i}\|)}}{\sum_i
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\frac{\lambda_i(\mathbf{x})} {f(\|\mathbf{x} - \mathbf{p_i}\|)}}
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\textrm{ and } \beta(\mathbf{x})= \sum_i \lambda_i(\mathbf{x})
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\|\mathbf{x} - \mathbf{p_i}\|^2,$$
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\beta(\mathbf{x})} \mbox{ where } \alpha(\mathbf{x}) =
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\frac{\ccSum{i}{}{ \lambda_i(\mathbf{x}) \frac{\|\mathbf{x} -
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\mathbf{p_i}\|^2}{f(\|\mathbf{x} - \mathbf{p_i}\|)}}}{\ccSum{i}{}{
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\frac{\lambda_i(\mathbf{x})} {f(\|\mathbf{x} - \mathbf{p_i}\|)}}}
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\mbox{ and } \beta(\mathbf{x})= \ccSum{i}{}{ \lambda_i(\mathbf{x})
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\|\mathbf{x} - \mathbf{p_i}\|^2},$$
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where in Sibson's original work,
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$f(\|\mathbf{x} - \mathbf{p_i}\|) = \|\mathbf{x} - \mathbf{p_i}\|$.
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@ -77,8 +77,8 @@ Knowing the gradient $\mathbf{g_i}$ for all $\mathbf{p_i} \in
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exactly quadratic functions. This interpolant is not $C^1$ continuous
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in general. It is defined as follows:
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\begin{displaymath}
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I^1(\mathbf{x}) = \sum_i \lambda_i(\mathbf{x})
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(z_i + \frac{1}{2} \mathbf{g_i}^t (\mathbf{x} - \mathbf{p_i}))
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I^1(\mathbf{x}) = \ccSum{i}{}{ \lambda_i(\mathbf{x})
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(z_i + \frac{1}{2} \mathbf{g_i}^t (\mathbf{x} - \mathbf{p_i}))}
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\end{displaymath}
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@ -89,9 +89,9 @@ $f$ from the function values on the data sites. For the data point
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$\mathbf{p_i}$, we determine
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$$\mathbf{g_i}
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= \min_{\mathbf{g}}
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\sum_j
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\ccSum{j}{}{
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\frac{\lambda_j(\mathbf{p_i})}{\|\mathbf{p_i} - \mathbf{p_j}\|^2}
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\left( z_j - (z_i + \mathbf{g}^t (\mathbf{p_j} -\mathbf{p_i})) \right),
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\left( z_j - (z_i + \mathbf{g}^t (\mathbf{p_j} -\mathbf{p_i})) \right)},
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$$
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where $\lambda_j(\mathbf{p_i})$ is the natural neighbor coordinate
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of $\mathbf{p_i}$ with respect to $\mathbf{p_i}$ associated to
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@ -514,7 +514,7 @@ the case if and only if there are real coefficients
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$\lambda_1,\ldots,\lambda_n$ such that $p$ is a convex combination of
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$p_1,\ldots,p_n$:
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\[
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p = \sum_{j=1}^{n}~\lambda_j~p_j, \quad \sum_{j=1}^{n}~\lambda_j = 1,
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p = \ccSum{j=1}{n}{~\lambda_j~p_j}, \quad \ccSum{j=1}{n}{~\lambda_j} = 1,
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\quad \lambda_j \geq 0 \mbox{~for all $j$.}
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\]
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The problem of testing the existence of such $\lambda_j$ can
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@ -526,11 +526,11 @@ $h_1,\ldots,h_n,h$, we have
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\[q_j = h_j \cdot (p_j \mid 1) \mbox{~for all $j$, and~} q = h \cdot
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(p\mid 1).\] Now, nonnegative $\lambda_1,\ldots,\lambda_n$ are
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suitable coefficients for a convex combination if and only if
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\[\sum_{j=1}^n~ \lambda_j(p_j \mid 1) = (p\mid 1), \]
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\[\ccSum{j=1}{n}{~ \lambda_j(p_j \mid 1)} = (p\mid 1), \]
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equivalently, if there are $\mu_1,\ldots,\mu_n$
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(with $\mu_j = \lambda_j \cdot h/{h_j}$ for all $j$) such that
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\[
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\sum_{j=1}^n~\mu_j~q_j = q, \quad \mu_j \geq 0\mbox{~for all $j$}.
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\ccSum{j=1}{n}{~\mu_j~q_j} = q, \quad \mu_j \geq 0\mbox{~for all $j$}.
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\]
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The linear program now tests for the existence of nonnegative $\mu_j$
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@ -349,8 +349,8 @@ then $\lambda_i\geq 0$ ($\lambda_i\leq 0$, respectively).
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&&\leq 0 & \mbox{if $l_j=-\infty$.}
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\end{array}
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\]
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\item \[\qplambda^T\qpb \quad<\quad \sum_{j: \qplambda^TA_j <0} \qplambda^TA_j u_j
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\quad+\quad \sum_{j: \qplambda^TA_j >0} \qplambda^TA_j l_j.\]
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\item \[\qplambda^T\qpb \quad<\quad \ccSum{j: \qplambda^TA_j <0}{}{ \qplambda^TA_j u_j }
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\quad+\quad \ccSum{j: \qplambda^TA_j >0}{}{ \qplambda^TA_j l_j}.\]
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\end{enumerate}
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{\bf Proof:} Let us assume for the purpose of obtaining a contradiction
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@ -358,10 +358,10 @@ that there is a feasible solution $\qpx$. Then we get
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\[
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\begin{array}{lcll}
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0 &\geq& \qplambda^T(A\qpx -\qpb) & \mbox{(by $A\qpx\qprel \qpb$ and 1.)} \\
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&=& \sum_{j: \qplambda^TA_j <0} \qplambda^TA_j x_j
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\quad+\quad \sum_{j: \qplambda^TA_j >0} \qplambda^TA_j x_j - \qplambda^T \qpb \\
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&\geq& \sum_{j: \qplambda^TA_j <0} \qplambda^TA_j u_j
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\quad+\quad \sum_{j: \qplambda^TA_j >0} \qplambda^TA_j l_j - \qplambda^T \qpb &
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&=& \ccSum{j: \qplambda^TA_j <0}{}{ \qplambda^TA_j x_j }
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\quad+\quad \ccSum{j: \qplambda^TA_j >0}{}{ \qplambda^TA_j x_j} - \qplambda^T \qpb \\
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&\geq& \ccSum{j: \qplambda^TA_j <0}{}{ \qplambda^TA_j u_j }
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\quad+\quad \ccSum{j: \qplambda^TA_j >0}{}{ \qplambda^TA_j l_j} - \qplambda^T \qpb &
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\mbox{(by $\qpl\leq \qpx \leq \qpu$ and 2.)} \\
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&>& 0 & \mbox{(by 3.)},
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\end{array}
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