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\section*{Preface to \Rheolef\ version 6.0}
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\subsection*{What is new in \Rheolef\ 6.0 ?}
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The major main features are:
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\cindex{distributed computation}%
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\item support {\bf distributed achitectures}: the code looks sequential, is easy to read and write
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but can be run massively parallel and distributed, based on the MPI library.
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\item {\bf high order polynomial} approximation:
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$P_k$ basis are introduced in this version, for $k\geq 0$.
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This feature will be improved in the future developments.
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\cindex{characteristic method}%
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\cindex{mesh!adaptation}%
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\item {\bf mesh adaptation} and the {\bf charateristic method} are now available
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for {\bf three-dimensional} problems.
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In order to evoluate in these directions, internal data structures inside the library
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are completely rewritten in a different way, and thus this version is a completely new library.
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Conversely, the library and unix command interfaces was as less as possible modified.
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Nevertheless, the user will find some few backward incompatibilities:
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5.93 based codes will not directly compile with the 6.0 library version.
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Let us review how to move a code from 5.93 to 6.0 version.
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\subsection*{Moving to \Rheolef\ 6.0}
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\subsubsection*{1. Namespace}
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% ---------------------------
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\cindex{namespace!rheolef}%
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The \code{namespace rheolef} was already introduced in last 5.93 version.
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Recall that a code usually starts with:
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\begin{lstlisting}[numbers=none,frame=none]
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using namespace rheolef;
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% ----------------------------
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\subsubsection*{2. Environment}
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% ---------------------------
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\clindex{environment}%
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\toindex{library!boost}%
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\cindex{argc, argv, command line arguments}%
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The MPI library requires initialisation and the two command line arguments.
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This initialisation is performed via the \code{boost::mpi} class \code{environment}:
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The code entry point writes:
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\begin{lstlisting}[numbers=none,frame=none]
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int main (int argc, char** argv) {
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environment rheolef (argc,argv);
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% --------------------------------------------------
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\subsubsection*{3. Fields and forms data accessors}
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% -------------------------------------------------
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The accesses to unknown and blocked data was of a \code{field uh}
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was direct, as \code{uh.u} and \code{uh.b}.
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This access is no more possible in a distributed environment, as
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non-local value requests may be optimized and thus, read and
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write access may be controled thought accessors.
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These accessors are named \code{uh.u()} and \code{uh.b()}
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for read access, and \code{uh.set\_u()} and \code{uh.set\_b()}
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Similarly, a \code{form a} has accessors as \code{a.uu()}.
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A typical 5.93 code writes:
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\begin{lstlisting}[numbers=none,frame=none]
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ssk<Float> sa = ldlt(a.uu);
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uh.u = sa.solve (lh.u - a.ub*uh.b);
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and the corresponding 6.0 code is:
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\begin{lstlisting}[numbers=none,frame=none]
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uh.set_u() = sa.solve (lh.u() - a.ub()*uh.b());
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This major change in the library interface induces the most important
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work when porting to the 6.0 version.
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Notice also that the old \code{ssk<Float>} class has been
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supersetted by the \code{solver} class, that manages
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both direct and iterative solvers in a more effective way.
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For three-dimensional problems, the iterative solver is the default
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while direct solvers are used otherwise.
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\clindex{solver\_abtb}%
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In the same spirit, a \code{solver\_abtb} has been introduced,
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for Stokes-like mixed problem.
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These features facilitate the dimension-independent coding style
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provided by the \Rheolef\ library.
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% ---------------------------------------------------------------------------
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\subsubsection*{4. Distributed input and output streams}
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% --------------------------------------------------------------------------
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\cindex{variable!\code{din}}%
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\cindex{variable!\code{dout}}%
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\cindex{variable!\code{derr}}%
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Input and output {\em sequential} standard streams \code{cin}, \code{cout} and \code{cerr}
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may now replaced by {\em distributed} \Rheolef\ streams \code{din}, \code{dout} and \code{derr} as:
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\begin{lstlisting}[numbers=none,frame=none]
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\clindex{idiststream}%
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\clindex{odiststream}%
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These new streams are available togeher with the \code{idiststream} and \code{odiststream}
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classes of the \Rheolef\ library.
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\subsubsection*{5. File formats \file{.geo} and \code{.field} have changed}
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% --------------------------------------------------------------------------
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\fiindex{\file{.geo} mesh}%
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\fiindex{\file{.field} field}%
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\fiindex{\file{.field} multi-component field}%
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The \file{.geo} and \file{.field} file formats have changed.
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The \code{.mfield} is now obsolete: it has been merged into
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the \code{.field} format that supports now multi-component fields.
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Also, the corresponding \code{mfield} unix command is obsolete,
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as these features are integrated in the \code{field} unix command.
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%TODO: relire les anciens formats en sequentiel et les convertir
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At this early stage of the 6.0 version, it is not yet possible to read
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the old \code{.geo} format, but this backward compatibility will be
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% ---------------------------------------------------------------------------
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\subsubsection*{6. Space on a domain}
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% --------------------------------------------------------------------------
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A space defined on a domain~\code{"boundary"} of a mesh \code{omega}
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was defined in the 5.93 version as:
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\begin{lstlisting}[numbers=none,frame=none]
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space Wh (omega["boundary"], omega, "P1");
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\begin{lstlisting}[numbers=none,frame=none]
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space Wh (omega["boundary"], "P1");
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as the repetition of \code{omega} is no more required.
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doc/pusrman/preface-v6.tex
