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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">I'm looking at snes example ex19.c, on "nonlinear driven cavity multigrid 2d. You can also access it via the website ( <a href="http://www.mcs.anl.gov/petsc/petsc-3.4/src/snes/examples/tutorials/ex19.c.html" target="_blank">http://acts.nersc.gov/petsc/example3/ex19.c.html</a> )
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<div>There are three user defined local functions (<i> <span style="font-size: 10pt;">FormFunctionLocal, </span></i><i style="font-size: 10pt;">FormFunctionLocali, </i><i style="font-size: 10pt;">FormFunctionLocali4</i><i style="font-size: 10pt;"><span style="font-size: 10pt;"> </span></i><span style="font-size: 10pt;">)
that serves as discretized PDE operators declared before main, and is defined right after main. In the middle of the main, there are these four lines:</span></div>
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<pre><i><font color="#2040a0">1. ierr</font> <font color="4444FF">=</font> <font color="#2040a0">DMMGSetSNESLocal</font><font color="4444FF">(</font><font color="#2040a0">dmmg</font>,<font color="#2040a0">FormFunctionLocal</font>,<font color="#FF0000">0</font>,<font color="#2040a0">ad_FormFunctionLocal</font>,<font color="#2040a0">admf_FormFunctionLocal</font><font color="4444FF">)</font><font color="4444FF">;</font><font color="#2040a0">CHKERRQ</font><font color="4444FF">(</font><font color="#2040a0">ierr</font><font color="4444FF">)</font><font color="4444FF">;</font>
2. <font color="#2040a0">ierr</font> <font color="4444FF">=</font> <font color="#2040a0">DMMGSetFromOptions</font><font color="4444FF">(</font><font color="#2040a0">dmmg</font><font color="4444FF">)</font><font color="4444FF">;</font><font color="#2040a0">CHKERRQ</font><font color="4444FF">(</font><font color="#2040a0">ierr</font><font color="4444FF">)</font><font color="4444FF">;</font>
3. <font color="#2040a0">ierr</font> <font color="4444FF">=</font> <font color="#2040a0">DMMGSetSNESLocali</font><font color="4444FF">(</font><font color="#2040a0">dmmg</font>,<font color="#2040a0">FormFunctionLocali</font>,<font color="#FF0000">0</font>,<font color="#2040a0">admf_FormFunctionLocali</font><font color="4444FF">)</font><font color="4444FF">;</font><font color="#2040a0">CHKERRQ</font><font color="4444FF">(</font><font color="#2040a0">ierr</font><font color="4444FF">)</font><font color="4444FF">;</font>
4. <font color="#2040a0">ierr</font> <font color="4444FF">=</font> <font color="#2040a0">DMMGSetSNESLocalib</font><font color="4444FF">(</font><font color="#2040a0">dmmg</font>,<font color="#2040a0">FormFunctionLocali4</font>,<font color="#FF0000">0</font>,<font color="#2040a0">admfb_FormFunctionLocali4</font><font color="4444FF">)</font><font color="4444FF">;</font><font color="#2040a0">CHKERRQ</font><font color="4444FF">(</font><font color="#2040a0">ierr</font><font color="4444FF">)</font><font color="4444FF">;</font></i></pre>
<pre><font face="Tahoma"><span style="white-space: normal;">I have the following questions:</span></font></pre>
<pre><font face="Tahoma"><span style="white-space: normal;">1. What are </span></font><span style="font-family: Tahoma; font-size: 10pt;">ad_FormFunctionLocal, admf_FormFunctionLocal from line 1? They are not defined anywhere in ex19.c. Other terms such as </span><span style="font-family: Tahoma; font-size: 10pt;">admf_FormFunctionLocali and </span><span style="font-family: Tahoma; font-size: 10pt;">admfb_FormFunctionLocali4 are also not defined anywhere in the file. </span></pre>
<pre><span style="font-family: Tahoma; font-size: 10pt;">2. To me it seems like </span><span style="font-family: Tahoma; font-size: 10pt;">DMMGSetSNESLocal, </span><span style="font-family: Tahoma; font-size: 10pt;">DMMGSetSNESLocali, and </span><span style="font-family: Tahoma; font-size: 10pt;">DMMGSetSNESLocalib evaluates the function for all grid points, for a single grid point and for a single degree of freedom, respectively. But how does the process choose which one to use? </span></pre>
<pre><span style="font-family: Tahoma; font-size: 10pt;">Thanks! - Hui</span></pre>
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