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<html>
<head>
<title>
SPARSE_GRID_OPEN - Sparse Grids Based on Open Quadrature Rules
</title>
</head>
<body bgcolor="#EEEEEE" link="#CC0000" alink="#FF3300" vlink="#000055">
<h1 align = "center">
SPARSE_GRID_OPEN <br> Sparse Grids Based on Open Quadrature Rules
</h1>
<hr>
<p>
<b>SPARSE_GRID_OPEN</b>
is a FORTRAN90 library which
computes the location of points on a sparse grid
based on an open quadrature rule.
</p>
<p>
One way of looking at the construction of sparse grids is to assume
that we start out by constructing a (very dense) product grid.
We will assume for now that the <b>order</b>, that is, the number of
points used in each component grid, is the same for all dimensions.
Moreover, we will assume that the order is a power of 2 minus one,
so that we have a natural relationship between the order and
the logarithm base 2 of the order plus 1:
</p>
<p>
<pre><b>
order = 2<sup>( level + 1 )</sup> - 1
</b></pre>
</p>
<p>
Thus, if we allow <b>level</b> to grow, the <b>order</b> roughly
doubles, as follows:
<table border = "1">
<tr><th>Level</th><th>Order</th></tr>
<tr><td> 0</td><td> 1</th></tr>
<tr><td> 1</td><td> 3</th></tr>
<tr><td> 2</td><td> 7</th></tr>
<tr><td> 3</td><td> 15</th></tr>
<tr><td> 4</td><td> 31</th></tr>
<tr><td> 5</td><td> 63</th></tr>
<tr><td> 6</td><td> 127</th></tr>
<tr><td> 7</td><td> 255</th></tr>
<tr><td> 8</td><td> 511</th></tr>
<tr><td> 9</td><td> 1023</th></tr>
<tr><td> 10</td><td> 2047</th></tr>
</table>
</p>
<p>
To keep things simple, let us begin by supposing we are selecting
points for a grid to be used in an interpolation or quadrature rule.
If you successively compute the locations of the points of each
level, you will probably see that the points of a level
are all included in the grid associated with the next level.
(This is not guaranteed for all rules; it's simply a property
of the way most such grids are defined!).
</p>
<p>
This <b>nesting</b> property is very useful. For one thing,
it means that when if we've computed a grid of one level, and now
proceed to the next, then all the information associated with
the current level (point location, the value of functions at those
points) is still useful for the next level, and will save us
some computation time as well. This also means that, when we
have reached a particular level, all the previous levels are
still available to us, with no extra storage. These considerations
make it possible, for instance, to do efficient and convenient
error estimation.
</p>
<p>
When we move to a problem whose geometry is two-dimensional or
more, we can still take the same approach. However, when working
in multidimensional geometry, it is usually not a good idea to
form a grid using the product of 1D grids, especially when we
are determining the order using the idea of levels. Especially
in this case, if we go to the next level in each dimension, the
total number of points would increase by a factor of roughly
2 to the spatial dimension. Just a few such steps in, say,
6 dimensions, and we would be far beyond our computational capacity.
</p>
<p>
Instead, in multidimensions, the idea is to construct a <i>sparse
grid</i>, which can be thought of in one of two ways:
<ul>
<li>
the sparse gird is a logical sum of low order product grids;
each product grid has a total level (sum of the levels of the
1d rules) that is less than or equal to <b>level_max</b>;
</li>
<li>
the sparse grid is a very sparse selection of points from the
very high order product grid formed by using rules of level
<b>level_max</b> in each dimension.
</li>
</ul>
</p>
<p><i>
(There is still a lot of explaining to do to get from the one-dimensional
levels to the N-dimensional levels and the selection of the low-level
product grids that sum up to the sparse grid...)
</i></p>
<p>
Once the grid indices of the sparse grid points have been selected,
there are a variety of schemes for distributing the points. We
concentrate on two sets of schemes:
<p>
<p>
Uniform (equally spaced) open rules of order N over [0,1]:
<ul>
<li>
Newton Cotes Open: [ 1, 2, 3,..., N ] / ( N + 1 );<br>
does not include boundaries. Point spacing is 1/(N+1)<br>
First and last points are distance 1/N to the boundary.
</li>
</ul>
</p>
<p>
The uniform schemes are easy to understand. However, it has
been observed that greater accuracy and stability can be achieved
by arranging the points in a nonuniform way that tends to move
points towards the boundary and away from the center.
A common scheme uses the cosine function to do this, and can
be naturally derived from the uniform schemes.
</p>
<p>
Nonuniform open rules of order N over [-1,1]:
<ul>
<li>
Fejer Type 2:<br>
Theta = pi * [ 1, 2, 3,..., N ] / ( N + 1 );<br>
Points = cos ( theta );<br>
does not include boundaries.<br>
Analogue to the Newton Cotes Open Rule.
</li>
<li>
Gauss-Patterson:<br>
Starting with midpoint rule, then the Gauss rule of order 3,<br>
incremented at each new level by intermediate points,<br>
does not include boundaries.
</li>
</ul>
</p>
<p>
Note that a standard Gauss-Legendre quadrature rule will not be suitable
for use in constructing sparse grids, because rules of successively
greater levels are not naturally nested.
</p>
<h3 align = "center">
Licensing:
</h3>
<p>
The computer code and data files described and made available on this web page
are distributed under
<a href = "../../txt/gnu_lgpl.txt">the GNU LGPL license.</a>
</p>
<h3 align = "center">
Languages:
</h3>
<p>
<b>SPARSE_GRID_OPEN</b> is available in
<a href = "../../cpp_src/sparse_grid_open/sparse_grid_open.html">a C++ version</a> and
<a href = "../../f_src/sparse_grid_open/sparse_grid_open.html">a FORTRAN90 version</a> and
<a href = "../../m_src/sparse_grid_open/sparse_grid_open.html">a MATLAB version</a>.
</p>
<h3 align = "center">
Related Data and Programs:
</h3>
<p>
<a href = "../../m_src/cc_display/cc_display.html">
CC_DISPLAY</a>,
a MATLAB library which
can compute and display Clenshaw Curtis grids in two dimensions,
as well as sparse grids formed from sums of Clenshaw Curtis grids.
</p>
<p>
<a href = "../../datasets/quadrature_rules/quadrature_rules.html">
QUADRATURE_RULES</a>,
a dataset directory which
defines quadrature rules;
a number of examples of sparse grid quadrature rules are included.
</p>
<p>
<a href = "../../f_src/quadrule/quadrule.html">
QUADRULE</a>,
a FORTRAN90 library which
defines quadrature rules for
various intervals and weight functions.
</p>
<p>
<a href = "../../f_src/sgmga/sgmga.html">
SGMGA</a>,
a FORTRAN90 library which
creates sparse grids based on a mixture of 1D quadrature rules,
allowing anisotropic weights for each dimension.
</p>
<p>
<a href = "../../c_src/smolpack/smolpack.html">
SMOLPACK</a>,
a C library which
implements Novak and Ritter's method for estimating the integral
of a function over a multidimensional hypercube using sparse grids.
</p>
<p>
<a href = "../../datasets/sparse_grid_cc/sparse_grid_cc.html">
SPARSE_GRID_CC</a>,
a dataset directory which
contains the abscissas of sparse
grids based on a Clenshaw Curtis rule.
</p>
<p>
<a href = "../../datasets/sparse_grid_f2/sparse_grid_f2.html">
SPARSE_GRID_F2</a>,
a dataset directory which
conains the abscissas of sparse
grids based on a Fejer Type 2 rule.
</p>
<p>
<a href = "../../f_src/sparse_grid_gl/sparse_grid_gl.html">
SPARSE_GRID_GL</a>,
a FORTRAN90 library which
creates sparse grids based on Gauss-Legendre rules.
</p>
<p>
<a href = "../../datasets/sparse_grid_gp/sparse_grid_gp.html">
SPARSE_GRID_GP</a>,
a dataset directory which
contains the abscissas of sparse
grids based on a Gauss Patterson rule.
</p>
<p>
<a href = "../../f_src/sparse_grid_hermite/sparse_grid_hermite.html">
SPARSE_GRID_HERMITE</a>,
a FORTRAN90 library which
creates sparse grids based on Gauss-Hermite rules.
</p>
<p>
<a href = "../../f_src/sparse_grid_laguerre/sparse_grid_laguerre.html">
SPARSE_GRID_LAGUERRE</a>,
a FORTRAN90 library which
creates sparse grids based on Gauss-Laguerre rules.
</p>
<p>
<a href = "../../f_src/sparse_grid_mixed/sparse_grid_mixed.html">
SPARSE_GRID_MIXED</a>,
a FORTRAN90 library which
constructs a sparse grid using different rules in each spatial dimension.
</p>
<p>
<a href = "../../datasets/sparse_grid_ncc/sparse_grid_ncc.html">
SPARSE_GRID_NCC</a>,
a dataset directory which
contains files of the abscissas of sparse
grids based on a Newton Cotes closed rule.
</p>
<p>
<a href = "../../datasets/sparse_grid_nco/sparse_grid_nco.html">
SPARSE_GRID_NCO</a>,
a dataset directory which
contains the abscissas of sparse
grids based on a Newton Cotes open rule.
</p>
<p>
<a href = "../../m_src/spinterp/spinterp.html">
SPINTERP</a>,
a MATLAB library which
carries out piecewise multilinear hierarchical sparse grid interpolation;
an earlier version of this software is ACM TOMS Algorithm 847,
by Andreas Klimke;
</p>
<p>
<a href = "../../m_src/toms847/toms847.html">
TOMS847</a>,
a MATLAB library which
carries out piecewise multilinear hierarchical sparse grid interpolation;
this library is commonly called SPINTERP (version 2.1);
this is ACM TOMS Algorithm 847,
by Andreas Klimke;
</p>
<h3 align = "center">
Reference:
</h3>
<p>
<ol>
<li>
Volker Barthelmann, Erich Novak, Klaus Ritter,<br>
High Dimensional Polynomial Interpolation on Sparse Grids,<br>
Advances in Computational Mathematics,<br>
Volume 12, Number 4, 2000, pages 273-288.
</li>
<li>
Thomas Gerstner, Michael Griebel,<br>
Numerical Integration Using Sparse Grids,<br>
Numerical Algorithms,<br>
Volume 18, Number 3-4, 1998, pages 209-232.
</li>
<li>
Albert Nijenhuis, Herbert Wilf,<br>
Combinatorial Algorithms for Computers and Calculators,<br>
Second Edition,<br>
Academic Press, 1978,<br>
ISBN: 0-12-519260-6,<br>
LC: QA164.N54.
</li>
<li>
Fabio Nobile, Raul Tempone, Clayton Webster,<br>
A Sparse Grid Stochastic Collocation Method for Partial Differential
Equations with Random Input Data,<br>
SIAM Journal on Numerical Analysis,<br>
Volume 46, Number 5, 2008, pages 2309-2345.
</li>
<li>
Sergey Smolyak,<br>
Quadrature and Interpolation Formulas for Tensor Products of
Certain Classes of Functions,<br>
Doklady Akademii Nauk SSSR,<br>
Volume 4, 1963, pages 240-243.
</li>
<li>
Dennis Stanton, Dennis White,<br>
Constructive Combinatorics,<br>
Springer, 1986,<br>
ISBN: 0387963472,<br>
LC: QA164.S79.
</li>
</ol>
</p>
<h3 align = "center">
Source Code:
</h3>
<p>
<ul>
<li>
<a href = "sparse_grid_open.f90">sparse_grid_open.f90</a>,
the source code.
</li>
<li>
<a href = "sparse_grid_open.sh">sparse_grid_open.sh</a>,
commands to compile the source code.
</li>
</ul>
</p>
<h3 align = "center">
Examples and Tests:
</h3>
<p>
<ul>
<li>
<a href = "sparse_grid_open_prb.f90">sparse_grid_open_prb.f90</a>,
a sample calling program.
</li>
<li>
<a href = "sparse_grid_open_prb.sh">sparse_grid_open_prb.sh</a>,
commands to compile and run the sample program.
</li>
<li>
<a href = "sparse_grid_open_prb_output.txt">
sparse_grid_open_prb_output.txt</a>,
the output file.
</li>
</ul>
</p>
<h3 align = "center">
List of Routines:
</h3>
<p>
<ul>
<li>
<b>ABSCISSA_LEVEL_OPEN_ND:</b> first level at which given abscissa is generated.
</li>
<li>
<b>COMP_NEXT</b> computes the compositions of the integer N into K parts.
</li>
<li>
<b>F2_ABSCISSA</b> returns the I-th abscissa for the Fejer type 2 rule.
</li>
<li>
<b>GET_UNIT</b> returns a free FORTRAN unit number.
</li>
<li>
<b>GL_ABSCISSA</b> sets abscissas for "nested" Gauss-Legendre quadrature.
</li>
<li>
<b>GP_ABSCISSA</b> returns the I-th abscissa for a Gauss Patterson rule.
</li>
<li>
<b>I4_CHOOSE</b> computes the binomial coefficient C(N,K).
</li>
<li>
<b>I4_MODP</b> returns the nonnegative remainder of I4 division.
</li>
<li>
<b>INDEX_TO_LEVEL_OPEN</b> determines the level of a point given its index.
</li>
<li>
<b>LEVEL_TO_ORDER_OPEN</b> converts a level to an order for open rules.
</li>
<li>
<b>LEVELS_OPEN_INDEX</b> computes open grids with 0 <= LEVEL <= LEVEL_MAX.
</li>
<li>
<b>MULTIGRID_INDEX1</b> returns an indexed multidimensional grid.
</li>
<li>
<b>MULTIGRID_SCALE_OPEN</b> renumbers a grid as a subgrid on a higher level.
</li>
<li>
<b>NCO_ABSCISSA</b> returns the I-th abscissa for the Newton Cotes Open rule.
</li>
<li>
<b>R8MAT_WRITE</b> writes an R8MAT file.
</li>
<li>
<b>S_BLANK_DELETE</b> removes blanks from a string, left justifying the remainder.
</li>
<li>
<b>SPARSE_GRID_F2S_SIZE</b> sizes a sparse grid using Fejer Type 2 Slow rules.
</li>
<li>
<b>SPARSE_GRID_GPS_SIZE</b> sizes a sparse grid using Gauss-Patterson-Slow rules.
</li>
<li>
<b>SPARSE_GRID_OFN_SIZE</b> sizes a sparse grid using Open Fully Nested rules.
</li>
<li>
<b>SPARSE_GRID_ONN_SIZE</b> sizes a sparse grid using Open Non-Nested rules.
</li>
<li>
<b>SPARSE_GRID_OWN_SIZE</b> sizes a sparse grid using Open Weakly Nested rules.
</li>
<li>
<b>TIMESTAMP</b> prints the current YMDHMS date as a time stamp.
</li>
<li>
<b>VEC_COLEX_NEXT2</b> generates vectors in colex order.
</li>
</ul>
</p>
<p>
You can go up one level to <a href = "../f_src.html">
the FORTRAN90 source codes</a>.
</p>
<hr>
<i>
Last revised on 12 January 2010.
</i>
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