Sometimes you will want to get data interpolated at specific points which might not be nodes. They might be points of physical significance, or a row or array of points for plotting. For this, the mark facility is useful. To use it, you need to prepare a file called mark.dat, with a listing of the points at which you wish to see results. These are listed with one set of coordinates per line and read into Fastflo with the command
mark 0Thereafter you can issue commands like mark 300. Interpolated values of the vectors that you name will appear in a table format in the file mark.out. The format is designed so that with a minimum of editing it can go into a plotting package such as gnuplot.
You can use this, for example, to plot results on plane sections of a 3D mesh. Make a 2D mesh file of the correct size for this section, perhaps using the tool Unit described in the next chapter. Then, with an editor, copy the list of point coordinates to a mark.dat file, and add a column of constants to make it a plane section in 3D.
Then run Fastflo with the 3D mesh to get the results you want to plot. Read in the mark.dat file with the command mark 0. If your editing has not made the 2D plane into the correct 3D section, you can apply mapmesh to the mesh, leaving the section unchanged. Then, with mark commands, print out the data you wish to plot.
You then have to edit the file back into the format of a stored data file. This requires removing the headings and coordinate values, and preceding each block of data by the location in which it is to be stored (such as V200). You can then run Fastflo with the 2D mesh file, reading in the data with a read command. The usual 2D graphics are then available.
This procedure is not automatic, but can be done readily in an editor like emacs that supports macros.