[Visualpython-users] How to plot only 'the last N points' using gcurve

[Hans F. <H.F...@so...>]

Dear all, I am trying to use gcurve to continuously display the last N
points of a scalar function. More concrete: a simulation goes through
a number of iterations and for each iteration, I'd like to plot one
scalar value. I want to display the last N points using gcurve.

Since I didn't see a way of deleting individual points from gcurve, I
have written the little class (appended below) which does nearly what
I want. What it doesn't do is to auto-scale the graph so that the last
N points are displayed in optimal resolution. I am happy to compute
the required min and max values for the y-axis myself but don't know
how to pass it to vpython in the correct way.

Can anybody help me? Or is this plotting of last N-points achievable
much easier using another approach?

Thank you,

Hans






import Numeric
import visual.graph

class PlotLastPoints:
     """plots the last N points of data that is provided subsequently.

     The first N-points are drawn using the usual
     vpython-gcurve(pos=[x,y]) method.

     After that, the first point is overwritten with the N+1 entry, the
     2nd point is replaced by the N+2 value etc.

     This is intended for a simulation where we have iterations on the
     x-axis, so the actual value there doesn't really matter.

     Bug: By not using gcurve's default mechanism for adding points,
     visual doesn't autoscale the graphs.
     """


     def __init__(self,N):
         self.N = N
         self.data=Numeric.zeros((N,),'d')
         self.last = 0
         self.disp=visual.graph.gdisplay(width=600,height=200)
         self.plot = visual.graph.gcurve()


         self.full = False  #have we more or exactly N points in self.data ?

     def update(self, E ):

         if self.full == False and (self.last == self.N):
             self.full = True

         if self.full:
             self.last = self.last % self.N
             self.data[self.last]=E
             self.plot.gcurve.x=Numeric.arange(self.N)[:]
             self.plot.gcurve.y=self.data[:]
         else:
             self.plot.plot(pos=[self.last,E])
             self.data[self.last]=E

         self.last +=1


if __name__=="__main__":


     import math,time

     plot = PlotLastPoints(50)

     for i in range(2000):
         plot.update( math.sin(i/50.0))
         time.sleep(0.02)