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<option>row, col</option>
<option>hes</option>
<option>work</option>
<option>n_sweep</option>
<option>VectorBase</option>
<option>VectorSet</option>
<option>---..Restrictions</option>
<option>VectorSize</option>
<option>Uses Forward</option>
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<center><b><big><big>Sparse Hessian: Easy Driver</big></big></b></center>
<br/>
<b><big><a name="Syntax" id="Syntax">Syntax</a></big></b>

<br/>

<code><i><font color="black"><span style='white-space: nowrap'>hes</span></font></i><font color="blue"><span style='white-space: nowrap'>&#xA0;=&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>f</span></font></i><font color="blue"><span style='white-space: nowrap'>.SparseHessian(</span></font><i><font color="black"><span style='white-space: nowrap'>x</span></font></i><font color="blue"><span style='white-space: nowrap'>,&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>w</span></font></i><font color="blue"><span style='white-space: nowrap'>)<br/>
</span></font><i><font color="black"><span style='white-space: nowrap'>hes</span></font></i><font color="blue"><span style='white-space: nowrap'>&#xA0;=&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>f</span></font></i><font color="blue"><span style='white-space: nowrap'>.SparseHessian(</span></font><i><font color="black"><span style='white-space: nowrap'>x</span></font></i><font color="blue"><span style='white-space: nowrap'>,&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>w</span></font></i><font color="blue"><span style='white-space: nowrap'>,&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>p</span></font></i><font color="blue"><span style='white-space: nowrap'>)<br/>
</span></font><i><font color="black"><span style='white-space: nowrap'>n_sweep</span></font></i><font color="blue"><span style='white-space: nowrap'>&#xA0;=&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>f</span></font></i><font color="blue"><span style='white-space: nowrap'>.SparseHessian(</span></font><i><font color="black"><span style='white-space: nowrap'>x</span></font></i><font color="blue"><span style='white-space: nowrap'>,&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>w</span></font></i><font color="blue"><span style='white-space: nowrap'>,&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>p</span></font></i><font color="blue"><span style='white-space: nowrap'>,&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>row</span></font></i><font color="blue"><span style='white-space: nowrap'>,&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>col</span></font></i><font color="blue"><span style='white-space: nowrap'>,&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>hes</span></font></i><font color="blue"><span style='white-space: nowrap'>,&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>work</span></font></i><font color="blue"><span style='white-space: nowrap'>)<br/>
</span></font></code>
<br/>
<b><big><a name="Purpose" id="Purpose">Purpose</a></big></b>
<br/>
We use 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>n</mi>
</mrow></math>

 for the <a href="seq_property.xml#Domain" target="_top"><span style='white-space: nowrap'>domain</span></a>
 size,
and 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>m</mi>
</mrow></math>

 for the <a href="seq_property.xml#Range" target="_top"><span style='white-space: nowrap'>range</span></a>
 size of 
<code><i><font color="black"><span style='white-space: nowrap'>f</span></font></i></code>
.
We use 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>F</mi>
<mo stretchy="false">:</mo>
<msup><mrow><mstyle mathvariant='bold'><mi mathvariant='bold'>R</mi>
</mstyle></mrow>
<mi mathvariant='italic'>n</mi>
</msup>
<mo stretchy="false">&#x02192;</mo>
<msup><mrow><mstyle mathvariant='bold'><mi mathvariant='bold'>R</mi>
</mstyle></mrow>
<mi mathvariant='italic'>m</mi>
</msup>
</mrow></math>

 do denote the
<a href="glossary.xml#AD Function" target="_top"><span style='white-space: nowrap'>AD&#xA0;function</span></a>

corresponding to 
<code><i><font color="black"><span style='white-space: nowrap'>f</span></font></i></code>
. 
The syntax above sets 
<code><i><font color="black"><span style='white-space: nowrap'>hes</span></font></i></code>
 to the Hessian 

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block"><mrow>
<mi mathvariant='italic'>H</mi>
<mo stretchy="false">(</mo>
<mi mathvariant='italic'>x</mi>
<mo stretchy="false">)</mo>
<mo stretchy="false">=</mo>
<mfrac><mrow><msup><mrow><mstyle mathvariant='normal'><mi mathvariant='normal'>d</mi>
</mstyle></mrow>
<mrow><mn>2</mn>
</mrow>
</msup>
</mrow>
<mrow><mrow><mstyle mathvariant='normal'><mi mathvariant='normal'>d</mi>
</mstyle></mrow>
<mspace width='.18em'/>
<msup><mrow><mi mathvariant='italic'>x</mi>
</mrow>
<mrow><mn>2</mn>
</mrow>
</msup>
</mrow>
</mfrac>
<munderover><mo displaystyle='true' largeop='true'>&#x02211;</mo>
<mrow><mi mathvariant='italic'>i</mi>
<mo stretchy="false">=</mo>
<mn>1</mn>
</mrow>
<mi mathvariant='italic'>m</mi>
</munderover>
<msub><mi mathvariant='italic'>w</mi>
<mi mathvariant='italic'>i</mi>
</msub>
<msub><mi mathvariant='italic'>F</mi>
<mi mathvariant='italic'>i</mi>
</msub>
<mo stretchy="false">(</mo>
<mi mathvariant='italic'>x</mi>
<mo stretchy="false">)</mo>
</mrow></math>

This routine takes advantage of the sparsity of the Hessian
in order to reduce the amount of computation necessary.
If 
<code><i><font color="black"><span style='white-space: nowrap'>row</span></font></i></code>
 and 
<code><i><font color="black"><span style='white-space: nowrap'>col</span></font></i></code>
 are present, it also takes
advantage of the reduced set of elements of the Hessian that
need to be computed.
One can use speed tests (e.g. <a href="speed_test.xml" target="_top"><span style='white-space: nowrap'>speed_test</span></a>
)
to verify that results are computed faster
than when using the routine <a href="hessian.xml" target="_top"><span style='white-space: nowrap'>Hessian</span></a>
.

<br/>
<br/>
<b><big><a name="f" id="f">f</a></big></b>
<br/>
The object 
<code><i><font color="black"><span style='white-space: nowrap'>f</span></font></i></code>
 has prototype

<code><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;ADFun&lt;</span></font><i><font color="black"><span style='white-space: nowrap'>Base</span></font></i><font color="blue"><span style='white-space: nowrap'>&gt;&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>f</span></font></i><font color="blue"><span style='white-space: nowrap'><br/>
</span></font></code>
Note that the <a href="adfun.xml" target="_top"><span style='white-space: nowrap'>ADFun</span></a>
 object 
<code><i><font color="black"><span style='white-space: nowrap'>f</span></font></i></code>
 is not <code><font color="blue">const</font></code>
(see <a href="sparse_hessian.xml#Uses Forward" target="_top"><span style='white-space: nowrap'>Uses&#xA0;Forward</span></a>
 below).

<br/>
<br/>
<b><big><a name="x" id="x">x</a></big></b>
<br/>
The argument 
<code><i><font color="black"><span style='white-space: nowrap'>x</span></font></i></code>
 has prototype

<code><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;const&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>VectorBase</span></font></i><font color="blue"><span style='white-space: nowrap'>&amp;&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>x</span></font></i><font color="blue"><span style='white-space: nowrap'><br/>
</span></font></code>
(see <a href="sparse_hessian.xml#VectorBase" target="_top"><span style='white-space: nowrap'>VectorBase</span></a>
 below)
and its size 
must be equal to 
<code><i><font color="black"><span style='white-space: nowrap'>n</span></font></i></code>
, the dimension of the
<a href="seq_property.xml#Domain" target="_top"><span style='white-space: nowrap'>domain</span></a>
 space for 
<code><i><font color="black"><span style='white-space: nowrap'>f</span></font></i></code>
.
It specifies
that point at which to evaluate the Hessian.

<br/>
<br/>
<b><big><a name="w" id="w">w</a></big></b>
<br/>
The argument 
<code><i><font color="black"><span style='white-space: nowrap'>w</span></font></i></code>
 has prototype

<code><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;const&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>VectorBase</span></font></i><font color="blue"><span style='white-space: nowrap'>&amp;&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>w</span></font></i><font color="blue"><span style='white-space: nowrap'><br/>
</span></font></code>
and size 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>m</mi>
</mrow></math>

.
It specifies the value of 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<msub><mi mathvariant='italic'>w</mi>
<mi mathvariant='italic'>i</mi>
</msub>
</mrow></math>

 in the expression 
for 
<code><i><font color="black"><span style='white-space: nowrap'>hes</span></font></i></code>
.
The more components of 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>w</mi>
</mrow></math>

 that are identically zero,
the more sparse the resulting Hessian may be (and hence the more efficient
the calculation of 
<code><i><font color="black"><span style='white-space: nowrap'>hes</span></font></i></code>
 may be).

<br/>
<br/>
<b><big><a name="p" id="p">p</a></big></b>
<br/>
The argument 
<code><i><font color="black"><span style='white-space: nowrap'>p</span></font></i></code>
 is optional and has prototype

<code><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;const&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>VectorSet</span></font></i><font color="blue"><span style='white-space: nowrap'>&amp;&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>p</span></font></i><font color="blue"><span style='white-space: nowrap'><br/>
</span></font></code>
(see <a href="sparse_hessian.xml#VectorSet" target="_top"><span style='white-space: nowrap'>VectorSet</span></a>
 below)
If it has elements of type <code><font color="blue">bool</font></code>,
its size is 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>n</mi>
<mo stretchy="false">*</mo>
<mi mathvariant='italic'>n</mi>
</mrow></math>

.
If it has elements of type <code><font color="blue">std::set&lt;size_t&gt;</font></code>,
its size is 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>n</mi>
</mrow></math>

 and all its set elements are between
zero and 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>n</mi>
<mo stretchy="false">-</mo>
<mn>1</mn>
</mrow></math>

.
It specifies a
<a href="glossary.xml#Sparsity Pattern" target="_top"><span style='white-space: nowrap'>sparsity&#xA0;pattern</span></a>
 
for the Hessian 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>H</mi>
<mo stretchy="false">(</mo>
<mi mathvariant='italic'>x</mi>
<mo stretchy="false">)</mo>
</mrow></math>

.
<code><span style='white-space: nowrap'><br/>
<br/>
</span></code>If this sparsity pattern does not change between calls to 

<code><font color="blue"><span style='white-space: nowrap'>SparseHessian</span></font></code>
, it should be faster to calculate 
<code><i><font color="black"><span style='white-space: nowrap'>p</span></font></i></code>
 once and
pass this argument to 
<code><font color="blue"><span style='white-space: nowrap'>SparseHessian</span></font></code>
.
In addition,
if you specify 
<code><i><font color="black"><span style='white-space: nowrap'>p</span></font></i></code>
, CppAD will use the same
type of sparsity representation
(vectors of <code><font color="blue">bool</font></code> or vectors of <code><font color="blue">std::set&lt;size_t&gt;</font></code>)
for its internal calculations.
Otherwise, the representation
for the internal calculations is unspecified.

<br/>
<br/>
<b><big><a name="row, col" id="row, col">row, col</a></big></b>
<br/>
The arguments 
<code><i><font color="black"><span style='white-space: nowrap'>row</span></font></i></code>
 and 
<code><i><font color="black"><span style='white-space: nowrap'>col</span></font></i></code>
 are optional and have prototype

<code><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;const&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>VectorSize</span></font></i><font color="blue"><span style='white-space: nowrap'>&amp;&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>row</span></font></i><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;const&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>VectorSize</span></font></i><font color="blue"><span style='white-space: nowrap'>&amp;&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>col</span></font></i><font color="blue"><span style='white-space: nowrap'><br/>
</span></font></code>
(see <a href="sparse_hessian.xml#VectorSize" target="_top"><span style='white-space: nowrap'>VectorSize</span></a>
 below).
They specify which rows and columns of 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>H</mi>
<mo stretchy="false">(</mo>
<mi mathvariant='italic'>x</mi>
<mo stretchy="false">)</mo>
</mrow></math>

 are
returned and in what order.
We use 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>K</mi>
</mrow></math>

 to denote the value 
<code><i><font color="black"><span style='white-space: nowrap'>hes</span></font></i><font color="blue"><span style='white-space: nowrap'>.size()</span></font></code>

which must also equal the size of 
<code><i><font color="black"><span style='white-space: nowrap'>row</span></font></i></code>
 and 
<code><i><font color="black"><span style='white-space: nowrap'>col</span></font></i></code>
.
Furthermore,
for 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>k</mi>
<mo stretchy="false">=</mo>
<mn>0</mn>
<mo stretchy="false">,</mo>
<mo stretchy="false">&#x02026;</mo>
<mo stretchy="false">,</mo>
<mi mathvariant='italic'>K</mi>
<mn>-1</mn>
</mrow></math>

, it must hold that

<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>row</mi>
<mo stretchy="false">[</mo>
<mi mathvariant='italic'>k</mi>
<mo stretchy="false">]</mo>
<mo stretchy="false">&lt;</mo>
<mi mathvariant='italic'>n</mi>
</mrow></math>

 and 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>col</mi>
<mo stretchy="false">[</mo>
<mi mathvariant='italic'>k</mi>
<mo stretchy="false">]</mo>
<mo stretchy="false">&lt;</mo>
<mi mathvariant='italic'>n</mi>
</mrow></math>

.
In addition, 
all of the 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mo stretchy="false">(</mo>
<mi mathvariant='italic'>row</mi>
<mo stretchy="false">[</mo>
<mi mathvariant='italic'>k</mi>
<mo stretchy="false">]</mo>
<mo stretchy="false">,</mo>
<mi mathvariant='italic'>col</mi>
<mo stretchy="false">[</mo>
<mi mathvariant='italic'>k</mi>
<mo stretchy="false">]</mo>
<mo stretchy="false">)</mo>
</mrow></math>

 pairs must correspond to a true value
in the sparsity pattern 
<code><i><font color="black"><span style='white-space: nowrap'>p</span></font></i></code>
.

<br/>
<br/>
<b><big><a name="hes" id="hes">hes</a></big></b>
<br/>
The result 
<code><i><font color="black"><span style='white-space: nowrap'>hes</span></font></i></code>
 has prototype

<code><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>VectorBase</span></font></i><font color="blue"><span style='white-space: nowrap'>&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>hes</span></font></i><font color="blue"><span style='white-space: nowrap'><br/>
</span></font></code>
In the case where 
<code><i><font color="black"><span style='white-space: nowrap'>row</span></font></i></code>
 and 
<code><i><font color="black"><span style='white-space: nowrap'>col</span></font></i></code>
 are not present,
the size of 
<code><i><font color="black"><span style='white-space: nowrap'>hes</span></font></i></code>
 is 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>n</mi>
<mo stretchy="false">*</mo>
<mi mathvariant='italic'>n</mi>
</mrow></math>

 and
its size is 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>n</mi>
<mo stretchy="false">*</mo>
<mi mathvariant='italic'>n</mi>
</mrow></math>

.
In this case, for 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>i</mi>
<mo stretchy="false">=</mo>
<mn>0</mn>
<mo stretchy="false">,</mo>
<mo stretchy="false">&#x02026;</mo>
<mo stretchy="false">,</mo>
<mi mathvariant='italic'>n</mi>
<mo stretchy="false">-</mo>
<mn>1</mn>
</mrow></math>

 
and 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>ell</mi>
<mo stretchy="false">=</mo>
<mn>0</mn>
<mo stretchy="false">,</mo>
<mo stretchy="false">&#x02026;</mo>
<mo stretchy="false">,</mo>
<mi mathvariant='italic'>n</mi>
<mo stretchy="false">-</mo>
<mn>1</mn>
</mrow></math>



<math xmlns="http://www.w3.org/1998/Math/MathML" display="block"><mrow>
<mi mathvariant='italic'>hes</mi>
<mo stretchy="false">[</mo>
<mi mathvariant='italic'>j</mi>
<mo stretchy="false">*</mo>
<mi mathvariant='italic'>n</mi>
<mo stretchy="false">+</mo>
<mo stretchy="false">&#x02113;</mo>
<mo stretchy="false">]</mo>
<mo stretchy="false">=</mo>
<mfrac><mrow><msup><mo stretchy="false">&#x02202;</mo>
<mn>2</mn>
</msup>
<msup><mi mathvariant='italic'>w</mi>
<mrow><mstyle mathvariant='normal'><mi mathvariant='normal'>T</mi>
</mstyle></mrow>
</msup>
<mi mathvariant='italic'>F</mi>
</mrow>
<mrow><mo stretchy="false">&#x02202;</mo>
<msub><mi mathvariant='italic'>x</mi>
<mi mathvariant='italic'>j</mi>
</msub>
<mo stretchy="false">&#x02202;</mo>
<msub><mi mathvariant='italic'>x</mi>
<mo stretchy="false">&#x02113;</mo>
</msub>
</mrow>
</mfrac>
<mo stretchy="false">(</mo>
<mi mathvariant='italic'>x</mi>
<mo stretchy="false">)</mo>
</mrow></math>

<code><span style='white-space: nowrap'><br/>
<br/>
</span></code>In the case where the arguments 
<code><i><font color="black"><span style='white-space: nowrap'>row</span></font></i></code>
 and 
<code><i><font color="black"><span style='white-space: nowrap'>col</span></font></i></code>
 are present,
we use 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>K</mi>
</mrow></math>

 to denote the size of 
<code><i><font color="black"><span style='white-space: nowrap'>hes</span></font></i></code>
. 
The input value of its elements does not matter.
Upon return, for 
<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow>
<mi mathvariant='italic'>k</mi>
<mo stretchy="false">=</mo>
<mn>0</mn>
<mo stretchy="false">,</mo>
<mo stretchy="false">&#x02026;</mo>
<mo stretchy="false">,</mo>
<mi mathvariant='italic'>K</mi>
<mo stretchy="false">-</mo>
<mn>1</mn>
</mrow></math>

,

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block"><mrow>
<mi mathvariant='italic'>hes</mi>
<mo stretchy="false">[</mo>
<mi mathvariant='italic'>k</mi>
<mo stretchy="false">]</mo>
<mo stretchy="false">=</mo>
<mfrac><mrow><msup><mo stretchy="false">&#x02202;</mo>
<mn>2</mn>
</msup>
<msup><mi mathvariant='italic'>w</mi>
<mrow><mstyle mathvariant='normal'><mi mathvariant='normal'>T</mi>
</mstyle></mrow>
</msup>
<mi mathvariant='italic'>F</mi>
</mrow>
<mrow><mo stretchy="false">&#x02202;</mo>
<msub><mi mathvariant='italic'>x</mi>
<mi mathvariant='italic'>j</mi>
</msub>
<mo stretchy="false">&#x02202;</mo>
<msub><mi mathvariant='italic'>x</mi>
<mo stretchy="false">&#x02113;</mo>
</msub>
</mrow>
</mfrac>
<mo stretchy="false">(</mo>
<mi mathvariant='italic'>x</mi>
<mo stretchy="false">)</mo>
<mspace width='.3em'/>
<mo stretchy="false">,</mo>
<mspace width='.3em'/>
<mspace width='.3em'/>
<mrow><mstyle mathvariant='normal'><mi mathvariant='normal'>where</mi>
</mstyle></mrow>
<mspace width='.3em'/>
<mi mathvariant='italic'>j</mi>
<mo stretchy="false">=</mo>
<mi mathvariant='italic'>row</mi>
<mo stretchy="false">[</mo>
<mi mathvariant='italic'>k</mi>
<mo stretchy="false">]</mo>
<mspace width='.3em'/>
<mrow><mstyle mathvariant='normal'><mi mathvariant='normal'>and</mi>
</mstyle></mrow>
<mspace width='.3em'/>
<mo stretchy="false">&#x02113;</mo>
<mo stretchy="false">=</mo>
<mi mathvariant='italic'>col</mi>
<mo stretchy="false">[</mo>
<mi mathvariant='italic'>k</mi>
<mo stretchy="false">]</mo>
</mrow></math>

<br/>
<b><big><a name="work" id="work">work</a></big></b>
<br/>
If this argument is present, it has prototype

<code><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;sparse_hessian_work&amp;&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>work</span></font></i><font color="blue"><span style='white-space: nowrap'><br/>
</span></font></code>
This object can only be used with the routines <code><font color="blue">SparseHessian</font></code>.
During its the first use, information is stored in 
<code><i><font color="black"><span style='white-space: nowrap'>work</span></font></i></code>
.
This is used to reduce the work done by future calls to <code><font color="blue">SparseHessian</font></code> 
with the same 
<code><i><font color="black"><span style='white-space: nowrap'>f</span></font></i></code>
, 
<code><i><font color="black"><span style='white-space: nowrap'>p</span></font></i></code>
, 
<code><i><font color="black"><span style='white-space: nowrap'>row</span></font></i></code>
, and 
<code><i><font color="black"><span style='white-space: nowrap'>col</span></font></i></code>
.
If a future call is make where any of these values have changed,
you must first call 
<code><i><font color="black"><span style='white-space: nowrap'>work</span></font></i><font color="blue"><span style='white-space: nowrap'>.clear()</span></font></code>

to inform CppAD that this information needs to be recomputed.

<br/>
<br/>
<b><big><a name="n_sweep" id="n_sweep">n_sweep</a></big></b>
<br/>
The return value 
<code><i><font color="black"><span style='white-space: nowrap'>n_sweep</span></font></i></code>
 has prototype

<code><font color="blue"><span style='white-space: nowrap'><br/>
&#xA0;&#xA0;&#xA0;&#xA0;&#xA0;size_t&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>n_sweep</span></font></i><font color="blue"><span style='white-space: nowrap'><br/>
</span></font></code>
It is the number of first order forward sweeps 
used to compute the requested Hessian values.
Each first forward sweep is followed by a second order reverse sweep 
so it is also the number of reverse sweeps.
This is proportional to the total work that <code><font color="blue">SparseHessian</font></code> does, 
not counting the zero order forward sweep, 
or the work to combine multiple columns into a single 
forward-reverse sweep pair.

<br/>
<br/>
<b><big><a name="VectorBase" id="VectorBase">VectorBase</a></big></b>
<br/>
The type 
<code><i><font color="black"><span style='white-space: nowrap'>VectorBase</span></font></i></code>
 must be a <a href="simplevector.xml" target="_top"><span style='white-space: nowrap'>SimpleVector</span></a>
 class with
<a href="simplevector.xml#Elements of Specified Type" target="_top"><span style='white-space: nowrap'>elements&#xA0;of&#xA0;type</span></a>


<code><i><font color="black"><span style='white-space: nowrap'>Base</span></font></i></code>
.
The routine <a href="checksimplevector.xml" target="_top"><span style='white-space: nowrap'>CheckSimpleVector</span></a>
 will generate an error message
if this is not the case.

<br/>
<br/>
<b><big><a name="VectorSet" id="VectorSet">VectorSet</a></big></b>
<br/>
The type 
<code><i><font color="black"><span style='white-space: nowrap'>VectorSet</span></font></i></code>
 must be a <a href="simplevector.xml" target="_top"><span style='white-space: nowrap'>SimpleVector</span></a>
 class with
<a href="simplevector.xml#Elements of Specified Type" target="_top"><span style='white-space: nowrap'>elements&#xA0;of&#xA0;type</span></a>

<code><font color="blue">bool</font></code> or <code><font color="blue">std::set&lt;size_t&gt;</font></code>;
see <a href="glossary.xml#Sparsity Pattern" target="_top"><span style='white-space: nowrap'>sparsity&#xA0;pattern</span></a>
 for a discussion
of the difference.
The routine <a href="checksimplevector.xml" target="_top"><span style='white-space: nowrap'>CheckSimpleVector</span></a>
 will generate an error message
if this is not the case.

<br/>
<br/>
<b><a name="VectorSet.Restrictions" id="VectorSet.Restrictions">Restrictions</a></b>
<br/>
If 
<code><i><font color="black"><span style='white-space: nowrap'>VectorSet</span></font></i></code>
 has elements of <code><font color="blue">std::set&lt;size_t&gt;</font></code>,
then 
<code><i><font color="black"><span style='white-space: nowrap'>p</span></font></i><font color="blue"><span style='white-space: nowrap'>[</span></font><i><font color="black"><span style='white-space: nowrap'>i</span></font></i><font color="blue"><span style='white-space: nowrap'>]</span></font></code>
 must return a reference (not a copy) to the 
corresponding set.
According to section 26.3.2.3 of the 1998 C++ standard,
<code><font color="blue">std::valarray&lt; std::set&lt;size_t&gt; &gt;</font></code> does not satisfy
this condition. 

<br/>
<br/>
<b><big><a name="VectorSize" id="VectorSize">VectorSize</a></big></b>
<br/>
The type 
<code><i><font color="black"><span style='white-space: nowrap'>VectorSize</span></font></i></code>
 must be a <a href="simplevector.xml" target="_top"><span style='white-space: nowrap'>SimpleVector</span></a>
 class with
<a href="simplevector.xml#Elements of Specified Type" target="_top"><span style='white-space: nowrap'>elements&#xA0;of&#xA0;type</span></a>

<code><font color="blue">size_t</font></code>.
The routine <a href="checksimplevector.xml" target="_top"><span style='white-space: nowrap'>CheckSimpleVector</span></a>
 will generate an error message
if this is not the case.

<br/>
<br/>
<b><big><a name="Uses Forward" id="Uses Forward">Uses Forward</a></big></b>
<br/>
After each call to <a href="forward.xml" target="_top"><span style='white-space: nowrap'>Forward</span></a>
,
the object 
<code><i><font color="black"><span style='white-space: nowrap'>f</span></font></i></code>
 contains the corresponding 
<a href="glossary.xml#Taylor Coefficient" target="_top"><span style='white-space: nowrap'>Taylor&#xA0;coefficients</span></a>
.
After a call to any of the sparse Hessian routines,
the zero order Taylor coefficients correspond to

<code><i><font color="black"><span style='white-space: nowrap'>f</span></font></i><font color="blue"><span style='white-space: nowrap'>.Forward(0,&#xA0;</span></font><i><font color="black"><span style='white-space: nowrap'>x</span></font></i><font color="blue"><span style='white-space: nowrap'>)</span></font></code>

and the other coefficients are unspecified.

<br/>
<br/>
<b><big><a name="Example" id="Example">Example</a></big></b>

<br/>
The routine
<a href="sparse_hessian.cpp.xml" target="_top"><span style='white-space: nowrap'>sparse_hessian.cpp</span></a>
 
is examples and tests of <code><font color="blue">sparse_hessian</font></code>.
It return <code><font color="blue">true</font></code>, if it succeeds and <code><font color="blue">false</font></code> otherwise.



<hr/>Input File: cppad/local/sparse_hessian.hpp

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