# Can't seem to plot 2 horizontal lines on same plot

I don't know what dumb thing I'm going but I can't seem to plot
2 horizontal lines on the same plot!!!

Why does this snippet give a *BLANK* plot when I run it?

(Either line separately seems to be ok!?!?)

import pylab
x1 = pylab.arange(-10, 10, 0.01)
x2 = pylab.arange( 0, 10, 0.01)
f1 = [0 for e in x1]
f2 = [1 for e in x2]
pylab.show(pylab.plot(x1, f1, x2, f2))

Chris

The autoscaling feature sets the y limits to [0,1] which means that
your lines are falling on the bottom and top x-axis which hides them.
Rescaling the y-axis will make the lines visible, e.g.

pylab.ylim(-1,2)

Johann

···

On Tuesday, 7 October 2008, chris@...1388... wrote:

Why does this snippet give a *BLANK* plot when I run it?

(Either line separately seems to be ok!?!?)

import pylab
x1 = pylab.arange(-10, 10, 0.01)
x2 = pylab.arange( 0, 10, 0.01)
f1 = [0 for e in x1]
f2 = [1 for e in x2]
pylab.show(pylab.plot(x1, f1, x2, f2))

pylab.show() takes no arguments. The pylab interface is "stateful", meaning you run a series of commands in order and it usually does the right thing, rather than passing the results of one function into another (in general).

Did you not get an exception when you ran your example?

The following works for me:

import pylab
x1 = pylab.arange(-10, 10, 0.01)
x2 = pylab.arange( 0, 10, 0.01)
f1 = [0 for e in x1]
f2 = [1 for e in x2]
pylab.plot(x1, f1, x2, f2)
pylab.show()

chris@...1388... wrote:

···

I don't know what dumb thing I'm going but I can't seem to plot
2 horizontal lines on the same plot!!!

Why does this snippet give a *BLANK* plot when I run it?

(Either line separately seems to be ok!?!?)

import pylab
x1 = pylab.arange(-10, 10, 0.01)
x2 = pylab.arange( 0, 10, 0.01)
f1 = [0 for e in x1]
f2 = [1 for e in x2]
pylab.show(pylab.plot(x1, f1, x2, f2))

Chris

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Michael Droettboom
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Space Telescope Science Institute
Operated by AURA for NASA

Thank you very much. That did it.

cs

···

On Tue, Oct 07, 2008 at 12:54:49PM +0200, Johann Rohwer wrote:

The autoscaling feature sets the y limits to [0,1] which means that
your lines are falling on the bottom and top x-axis which hides them.
Rescaling the y-axis will make the lines visible, e.g.

pylab.ylim(-1,2)

The lines aren't visible when I do it. No exceptions given.

cs

···

On Tue, Oct 07, 2008 at 08:19:39AM -0400, Michael Droettboom wrote:

Did you not get an exception when you ran your example?

The following works for me:

import pylab
x1 = pylab.arange(-10, 10, 0.01)
x2 = pylab.arange( 0, 10, 0.01)
f1 = [0 for e in x1]
f2 = [1 for e in x2]
pylab.plot(x1, f1, x2, f2)
pylab.show()