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<title>XPP - DIRECTION FIELD/FLOW</title>
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<h1><b>Direction Field/Flow </b></h1>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.<p>
<ul>
<li> <b> (D)irection fields </b> <br> 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.<p>
<li> <b> (F)low </b> <br> 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. <p> Any given trajectory can be aborted by pressing
<b>Esc</b> and the whole process stopped by pressing <b>/</b>. <p> The remaining
variables if in more than two-dimensions are initialized with the values in the IC window.<p>
<li> <b>(N)o Dir Field </b> <br> turns off redrawing of direction fields when you click on (Redraw). Erasing the screen automatically turns this off <p>
<li> <b>(C)olorize </b> <br> This draws a grid of filled rectangles on the screen whose color is coded by the velocity or some other quantity. (See the <a href=xppnumerics.html#color>Numerics|Color code</a> menu item). <p>
<li> <b>(S)caled Dir. Fld </b> <br> is the same as (D)irection field but the
lengths are all scaled to 1 so only directional information is given. <p>
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