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====== Differences ====== This shows you the differences between two versions of the page.

--- docs:classes:fieldsymmetry [2009/02/16 06:49]
gibson
+++ docs:classes:fieldsymmetry [2010/02/02 07:55] (current)
@@ Line 14: / Line 14: @@
 Let G be the group generated by these symmetries. Specific choice of boundary conditions at the walls
 might constrain the symmetry group of a specific flow to a subgroup G. But for generality,the FieldSymmetry
-class can represent any symmetry in G. The FieldSymmetry class parameterizes symmetries σ  symmetries as follows. Any element of the symmetry group is defined by six parameters
+class can represent any symmetry in G. The FieldSymmetry class parameterizes symmetries σ ⊂ G symmetries
+as follows. Any element of the symmetry group is defined by six parameters
 <latex> $ \begin{align*}
-  sigma &= (s_x, s_y, s_x, a_x, a_z, s)\\
+  \sigma &= (s_x, s_y, s_x, a_x, a_z, s)\\
-  sx, sy, sz, s &= \pm 1\\
+  s_x, s_y, s_z, s &= \pm 1\\
-  ax, az &\in [-0.5, 0.5)
+  a_x, a_z &\in [-0.5, 0.5)
 \end{align*} $ </latex>
-with the action of sigma on a velocity field u as
+with the action of σ on a velocity field u as
 <latex>
@@ Line 28: / Line 29: @@
 </latex>
-In C++ code, elements of the symmetry group can be defined as follows
+The following is a brief overview of FieldSymmetry functionality. For a complete description,
+see the header file {{:librarycode:symmetry.h}}.
+===== Constructors / Initialization =====
+In C++ code, elements of the symmetry group can initialized as follows,
+where %%sx,sy,sz%% are of type %%int%% and %%ax, az%% are of type %%Real%%.
 <code c++>
   FieldSymmetry sigma0(sx, sy, sz, ax, az, s);
-  FieldSymmetry sigma1(sx, sy, sz, ax, az);    // s defaults to 1
+  FieldSymmetry sigma1(sx, sy, sz, ax, az);  // the s argument s defaults to 1
-  FieldSymmetry sigma2(sx, sy, sz);            // s defaults to 1; ax,az to 0
+  FieldSymmetry sigma2(sx, sy, sz);          // s defaults to 1; ax,az to 0
-  FieldSymmetry tau(ax, az);     // pure translation: s,sx,sy,sz default to 1
+  FieldSymmetry tau(ax, az);                 // pure translation: s,sx,sy,sz default to 1
-  FieldSymmetry sigma3;          // the identity: s defaults to 1; ax,az to 0; sx,sy,sz to 1
+  FieldSymmetry identity;                    // the identity: s defaults to 1; ax,az to 0; sx,sy,sz to 1
 </code>
-where sx,sy,sz are of type int and ax, az are of type Real. FieldSymmetries act on each
+===== Operations =====
-other and velocity fields as follows
-<code>
+FieldSymmetries act on each other and velocity fields as follows
+<code c++>
   FieldSymmetry sigma4 = sigma2 * sigma1;     // group multiplication
@@ Line 52: / Line 59: @@
   FlowField u("u");                           // read velocity field u from disk
-  FlowField v = sigma1 * u;                   // v
+  FlowField v = sigma1 * u;                   // Make new field v = sigma1 u
   v *= sigma2;                                // v now equals sigma2 * sigma1 * u
 </code>
-FieldSymmetries can be saved to / read from disk as follows
+FieldSymmetries can be saved to / read from disk...
-<code>
+<code c++>
   sigma1.save("sigma1");                      // saves to ASCII file sigma1.asc
+  FieldSymmetry sigma7("sigma1");             // make a new symmetry element sigma7 == sigma1
 </code>
-Any element of G is of the form
+...compared to each other...
+<code c++>
+  if (sigma1 != identity)
+    ...
+  else if (sigma1 == sigma7)
+    ...
+</code>
+===== ASCII IO =====
+==== FieldSymmetry ====
+The FieldSymmetry uses ASCII input-output. The storage format is
+  s sx sy sz ax az
+Thus, the following C++ channelflow code
+<code c++>
+FieldSymmetry sigma(-1, -1, -1, 0.3, 0.1);
+sigma.save("sigma");
+</code>
+produces the ASCII file ''sigma.asc'' with contents
+-1 -1 -1 0.3 0.1
+which can then be read back into a channeflow program with
+<code c++>
+FieldSymmetry sigma("sigma");
+</code>
+Note that  the order of parameters in the ASCII file is different than the order in the ''FieldSymmetry'' constructor: the overall multiplicative sign ''s'' goes first in the file and last in the C++ constructor. I apologize for this. The reasons for the difference are are historical. The next release of channelflow will have order (s, sx, sy, sz, ax, az) for both.
+==== SymmetryList ====
+The ''SymmetryList'' class is a essentially an array of ''FieldSymmetry'' objects with simple ASCII IO methods. The ASCII format is
+   % N
+   s0 sx0 sy0 sz0 ax0 az0
+   s1 sx1 sy1 sz1 ax1 az1
+   ...
+where N is the number of symmetries listed in the file. Thus the file ''S.asc'' with contents
+   % 2
+  1  1 -1  0.5  0.0
+-1 -1  1  0.5  0.5
+represents the symmetries σ0 = (1, 1, 1, -1, 0.5, 0.0) and σ1 = (1, -1, -1,  1,  0.5,  0.5). These are the generators of the S
+[[docs:math:symmetry#isotropy_groups_of_known_solutions|S symmetry group]]. The generators can be loaded into channelflow, used, and saved as follows
+<code c++>
+SymmetryList S("S");      // load generators from ASCII file
+FlowField foo = S[0](u);  // apply (1,  1,  1, -1, 0.5, 0.0) to u
+FlowField bar = S[1](u);  // apply (1, -1, -1,  1, 0.5, 0.5) to u
+S.save("Q");              // save generators into another file
+SymmetryList P(4);        // Create another symmetry group
+P[0] = FieldSymmetry(1,1,1, 0.2, 0.0);
+P[1] = etc.;
+</code>

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