GfsFunction

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The GTS file must be a planar (preferably Delaunay) triangulation of a set of points. The value of the function at a given (x,y) coordinate is then calculated by computing the z-coordinate of the intersection of a vertical line passing through the point at (x,y,0) with the triangulation defined by the GTS file. The GTS file must be a planar (preferably Delaunay) triangulation of a set of points. The value of the function at a given (x,y) coordinate is then calculated by computing the z-coordinate of the intersection of a vertical line passing through the point at (x,y,0) with the triangulation defined by the GTS file.
 +
 +or a CDG file
 +
 + myfile.cdg
 +
 +The CDG file contain cartesian data. This type of file can be used to introduce 1 to 4 spacial time dimensions data.
 +The first line define the structure of grid for example :
 + 3 x y t
 +Here 3 show the number of dimension. x, y and t show the structure of data : 2 spacial dimensions and 1 temporal dimension.
 +The data is structured according to space vectors first and according to time vector finaly.
 +The 3 next lines defines the grid : each line contain one vector witch define the position of each point in space-time.
 +The rest of file contain the data.
 +More information in [http://en.wikipedia.org/wiki/cartesian_grid this page].
Gradients of variables can be computed using the <code>dx()</code>, <code>dy()</code> and <code>dz()</code> functions. For example, the z-component of the vorticity would be computed as: Gradients of variables can be computed using the <code>dx()</code>, <code>dy()</code> and <code>dz()</code> functions. For example, the z-component of the vorticity would be computed as:

Revision as of 11:05, 22 November 2007

Functions can be used in most objects which require a numerical parameter. A function can be a constant or a piece of C code taking coordinates (x,y,z), time t or any of the domain variables as arguments and returning a floating-point value.

The syntax in parameter files is as follows: 

-1.78e-3

or a C function 

{
  double a = sin (x + y);
  double b = cos (x - z);
  double c = sin (M_PI*t);
  return a + b + c;
}

or a C expression 

40.*(P - 1.)

or a GTS file 

myfunction.gts

The GTS file must be a planar (preferably Delaunay) triangulation of a set of points. The value of the function at a given (x,y) coordinate is then calculated by computing the z-coordinate of the intersection of a vertical line passing through the point at (x,y,0) with the triangulation defined by the GTS file.

or a CDG file 

myfile.cdg

The CDG file contain cartesian data. This type of file can be used to introduce 1 to 4 spacial time dimensions data. The first line define the structure of grid for example : 

3 x y t

Here 3 show the number of dimension. x, y and t show the structure of data : 2 spacial dimensions and 1 temporal dimension. The data is structured according to space vectors first and according to time vector finaly. The 3 next lines defines the grid : each line contain one vector witch define the position of each point in space-time. The rest of file contain the data. More information in this page.

Gradients of variables can be computed using the dx(), dy() and dz() functions. For example, the z-component of the vorticity would be computed as: 

(dx("V") - dy("U"))

More details on C functions

Comments should use the C syntax; i.e. opening /* and closing */ not necessarily on the same line rather than the usual parameter file syntax of a line beginning with a #. This is to allow the use of C preprocessor directives in C functions in GfsFunctions.

Example:

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