Re: graphing equations

[Przemek Klosowski]

   > to plot three planes on the same graph. for example
   > 2x+y+z=4  x+y+z=2  3x-y-z=2 so students can see the point of intersection.

Since Octave is a numerical environment, it assumes that you want to plot
numerical objects (arrays of data). Plotting functions, then, requires
manually preparing the 'support' arrays and calculating the value arrays:

         x = 0:.1:pi
         plot(sin(x))
or       plot(cos(0:.1:pi)

this gets even longer for 2-d support:

         [x,y]=meshdom(0:.1:pi, 0:.1:pi)
         mesh(x,y,sin(x.*y))

Using gnuplot directly, you can simplify it a little bit because gnuplot
can plot functions: you can just say 

    splot 4-2*x-y,2-x-y,3*x-y+2

and it will plot what you need (the default range is [-10:10]x[-10:10])



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