XPP - DIRECTION FIELD/FLOW

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# Direction Field/Flow

This option is best used for two-dimensional systems however, it can be applied to any system. The current graphics view must be a two-d plot in which both variables are different and neithet is the time variable, T. There are five items.

- (D)irection fields
  Choosing the direction field option will prompt you for a grid size. The two dimensional plane is broken into a grid of the size specified and lines are drwan at each point specifying the direction of the flow at that point. If the system is more than two-dimensional, the other variables will be held at the values in the initial conditions window.

- (F)low
  Choosing the flow, you will be prompted for a grid size and trajectories started at each point on the grid will be integrated according to the numerical parameters.

  Any given trajectory can be aborted by pressing Esc and the whole process stopped by pressing /.

  The remaining variables if in more than two-dimensions are initialized with the values in the IC window.

- (N)o Dir Field
  turns off redrawing of direction fields when you click on (Redraw). Erasing the screen automatically turns this off

- (C)olorize
  This draws a grid of filled rectangles on the screen whose color is coded by the velocity or some other quantity. (See the Numerics|Color code menu item).

- (S)caled Dir. Fld
  is the same as (D)irection field but the lengths are all scaled to 1 so only directional information is given.