please help with arrow drawing.

Hi all
I want to draw an two headed arrow between two points.
But I get a line. What I am doing wrong? I actually try to plot an
image similar to this one:
http://upload.wikimedia.org/wikipedia/commons/a/a3/Parameters_of_the_Marcus_Equation.JPG
may be I can use an annotate function for this.
Thanks for help.
Petro.

···

########
import pylab
from scipy import optimize
import numpy
x1=numpy.arange(-4000,1000,0.1)
x2=numpy.arange(-1000,4000,0.1)
y1=100*numpy.square(x1+1500)
y2=100*numpy.square(x2-1500)-0.1e9
pylab.figure()
pylab.plot(x1,y1,x2,y2)
pylab.grid("True")
pylab.arrow(-3000,0,0,-100000000,width=1)
pylab.xlim(-5000,5000)
pylab.ylim(-2e8,7e8)
pylab.show()
###########x

As far as I know, the ‘arrow’ function is not recommended. The ‘annotate’ function has a lot more features. Here’s your code with the annotate function:

import pylab
from scipy import optimize
import numpy
x1=numpy.arange(-4000,1000,0.1)
x2=numpy.arange(-1000,4000,0.1)
y1=100numpy.square(x1+1500)
y2=100
numpy.square(x2-1500)-0.1e9
pylab.figure()

pylab.plot(x1,y1,x2,y2)
pylab.grid(True)

pylab.annotate(’’,(-3000,0),(-3000,-100000000),
arrowprops=dict(arrowstyle=’<->’))
pylab.xlim(-5000,5000)
pylab.ylim(-2e8,7e8)
pylab.show()

Hope that helps a little.

Ryan

···

On Mon, Oct 17, 2011 at 12:02 PM, Piter_ <x.piter@…287…> wrote:

Hi all
I want to draw an two headed arrow between two points.
But I get a line. What I am doing wrong? I actually try to plot an

image similar to this one:
http://upload.wikimedia.org/wikipedia/commons/a/a3/Parameters_of_the_Marcus_Equation.JPG

may be I can use an annotate function for this.
Thanks for help.
Petro.
########
import pylab
from scipy import optimize
import numpy
x1=numpy.arange(-4000,1000,0.1)
x2=numpy.arange(-1000,4000,0.1)

y1=100numpy.square(x1+1500)
y2=100
numpy.square(x2-1500)-0.1e9
pylab.figure()
pylab.plot(x1,y1,x2,y2)
pylab.grid(“True”)
pylab.arrow(-3000,0,0,-100000000,width=1)
pylab.xlim(-5000,5000)
pylab.ylim(-2e8,7e8)

pylab.show()
###########x


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