<h1>Results</h1>

<h2>Logfile output</h2>
First, the program produces the usual logfile here stored in <tt>deallog</tt>. It reads (with omission of intermediate steps)

@code
DEAL::Element: FE_DGQ<2>(3)
DEAL::Step 0
DEAL::Triangulation 4 cells, 1 levels
DEAL::DoFHandler 64 dofs, level dofs 64
DEAL::Assemble matrix
DEAL::Assemble multilevel matrix
DEAL::Assemble right hand side
DEAL::Solve
DEAL:cg::Starting value 27.1275
DEAL:cg::Convergence step 1 value 1.97998e-14
DEAL::Error    0.161172
DEAL::Estimate 1.35839
DEAL::Writing solution to <sol-00.gnuplot>...
DEAL::
DEAL::Step 1
DEAL::Triangulation 10 cells, 2 levels
DEAL::DoFHandler 160 dofs, level dofs 64 128
DEAL::Assemble matrix
DEAL::Assemble multilevel matrix
DEAL::Assemble right hand side
DEAL::Solve
DEAL:cg::Starting value 35.5356
DEAL:cg::Convergence step 14 value 3.21479e-13
DEAL::Error    0.164760
DEAL::Estimate 1.08528
DEAL::Writing solution to <sol-01.gnuplot>...
DEAL::
DEAL::Step 2
DEAL::Triangulation 16 cells, 2 levels
DEAL::DoFHandler 256 dofs, level dofs 64 256
DEAL::Assemble matrix
DEAL::Assemble multilevel matrix
DEAL::Assemble right hand side
DEAL::Solve
DEAL:cg::Starting value 37.0552
DEAL:cg::Convergence step 14 value 6.05416e-13
DEAL::Error    0.113503
DEAL::Estimate 0.990460
DEAL::Writing solution to <sol-02.gnuplot>...

...

DEAL::Step 10
DEAL::Triangulation 124 cells, 9 levels
DEAL::DoFHandler 1984 dofs, level dofs 64 256 512 512 256 256 256 256 256
DEAL::Assemble matrix
DEAL::Assemble multilevel matrix
DEAL::Assemble right hand side
DEAL::Solve
DEAL:cg::Starting value 38.5798
DEAL:cg::Convergence step 17 value 2.64999e-13
DEAL::Error    0.0101278
DEAL::Estimate 0.0957571
DEAL::Writing solution to <sol-10.gnuplot>...
DEAL::
DEAL::Step 11
DEAL::Triangulation 163 cells, 10 levels
DEAL::DoFHandler 2608 dofs, level dofs 64 256 768 576 512 256 256 256 256 256
DEAL::Assemble matrix
DEAL::Assemble multilevel matrix
DEAL::Assemble right hand side
DEAL::Solve
DEAL:cg::Starting value 44.1721
DEAL:cg::Convergence step 17 value 3.18657e-13
DEAL::Error    0.00716962
DEAL::Estimate 0.0681646
DEAL::Writing solution to <sol-11.gnuplot>...
DEAL::
@endcode

This log for instance shows that the number of conjugate gradient
iteration steps is constant at approximately 17.

<h2>Postprocessing of the logfile</h2>

<img src="http://www.dealii.org/images/steps/developer/step-39-convergence.png" alt="">
Using the perl script <tt>postprocess.pl</tt>, we extract relevant
data into <tt>output.dat</tt>, which can be used to plot graphs with
<tt>gnuplot</tt>. The graph above for instance was produced with

@code
set style data linespoints
set logscale
set xrange [50:3000]
plot "output.dat" using 2:3 title "error", "" using 2:4 title "estimate", \
     "" using 2:(3000*$2**-1.5) title "3rd order"
@endcode
