Editing IVAJ/Level1 (section)

==<font color="#0000DD">Customized Python Module</font>==
To make it possible for us to examine the properties of binary mass-transfer flows from reference frames that have a range of different angular frequencies of rotation, <math>\Omega_\mathrm{frame}  = (\Omega_0 + \Delta\Omega)</math>, we wrote a Python-based module &#150; <font face="Courier">SwitchCoord</font> &#150; for insertion into the base [http://www.vistrails.org VisTrails] workflow.  Figure 1c shows our resulting customized [http://www.vistrails.org VisTrails] workflow; it differs very little from the base workflow.  The [http://www.vistrails.org/index.php/User:Tohline/CustomizedPythonModule#Sidebar sidebar] shows the complete Python source code from our customized module.  The code segment that performs the required ''physics analysis'' is short and straightforward.  In particular, the <font face="Courier">SwitchCoord</font> module performs the following operations at each grid vertex:
* converts the <math>(x, y)</math> Cartesian to <math>(R, \phi)</math> cylindrical coordinates;
* divides the momentum components by density to obtain the velocity components if the density is greater than <font face="Courier">minp</font> (otherwise, it sets the velocity components to zero);
* shifts the azimuthal velocity component <math>v_\phi</math> to a new, rotating frame of reference by adding <math>R\times \Delta\Omega</math>;
* converts the cylindrical velocity components to Cartesian velocity components; and
* normalizes the velocities to the maximum velocity <font face="Courier">maxnorm</font> found across the domain where densities are greater than <font face="Courier">minp</font>.

We designed the output ports on <font face="Courier">SwitchCoord</font> to provide access to the same type of structured arrays that <font face="Courier">vtkPLOT3DReader</font> generates.  But, in our customized [http://www.vistrails.org VisTrails] workflow, which includes <font face="Courier">SwitchCoord</font> (see Figure 1c), the 3D vector field that [http://www.vistrails.org VisTrails] pipes into each of the eight <font face="Courier">Draw_Streamline</font> module groups represents the fluid's velocity distribution as viewed from the rotating frame of reference that the floating-point scalar, <font face="Courier">Omega_frame</font>, specifies.