matplotlib-users

[Matplotlib-users] Labels in a dynamic graph

[Amit F. <ami...@gm...>]

Hi everyone,


I am using matplotlib to dynamically plot a graph with both my x and y
points taken from a measurement device. That is to say, in each
iteration of my while loop I'm reading two variables which I then want
to plot with matplotlib.


I wrote something which goes like this (disregard the Gnuplot - that's
what I'm trying to replace with matplotlib...)



    import gpib, Numeric, time, Gnuplot, mymodule, threading
    from pylab import *

   

    def cooldown(filename, dmm_gpib, lake_gpib):

    """this program scans dummy and reads HP and Lakeshore"""

    A             = Numeric.arange(-1, 1, .1)
    delay         = 1
    f = open(filename,'w')


    X = []
    Y = []
    figure(2)
    hold(False)
        try:       
            while A[0]<10:

                gpib.write(lake_fd, 'SDAT?')
                gpib.write(hp_fd, 'read?')
                time.sleep(delay)
                val1 = float(gpib.read(lake_fd, 30))
                val2 = float(gpib.read(hp_fd, 30))
                X.append(val1)
                Y.append(val2)
                plot(X,Y,'.-')
                f.write(str(val1) + '\t' + str(val2) + '\n')
                f.flush()

I'm running this code in ipython with the -pylab option, so I don't need
to use show(). My question is, how do I maintain a *constant* xlabel and
ylabel without having to redraw them each time I append a point to the
graph? If I try xlabel('something') then obviously it's cleared each
time I use plot(X,Y).

Any ideas?

Thanks,

Amit.

Re: [Matplotlib-users] Labels in a dynamic graph

[Matthias M. <Mat...@gm...>]

Hello Amit,

On Sunday 23 March 2008 09:54, Amit Finkler wrote:
> Hi everyone,
>
>
> I am using matplotlib to dynamically plot a graph with both my x and y
> points taken from a measurement device. That is to say, in each
> iteration of my while loop I'm reading two variables which I then want
> to plot with matplotlib.
>
>
> I wrote something which goes like this (disregard the Gnuplot - that's
> what I'm trying to replace with matplotlib...)
>
>
>
>     import gpib, Numeric, time, Gnuplot, mymodule, threading
>     from pylab import *
>
>
>
>     def cooldown(filename, dmm_gpib, lake_gpib):
>
>     """this program scans dummy and reads HP and Lakeshore"""
>
>     A             = Numeric.arange(-1, 1, .1)
>     delay         = 1
>     f = open(filename,'w')
>
>
>     X = []
>     Y = []
>     figure(2)
>     hold(False)
>         try:
>             while A[0]<10:
>
>                 gpib.write(lake_fd, 'SDAT?')
>                 gpib.write(hp_fd, 'read?')
>                 time.sleep(delay)
>                 val1 = float(gpib.read(lake_fd, 30))
>                 val2 = float(gpib.read(hp_fd, 30))
>                 X.append(val1)
>                 Y.append(val2)
>                 plot(X,Y,'.-')
>                 f.write(str(val1) + '\t' + str(val2) + '\n')
>                 f.flush()
>
> I'm running this code in ipython with the -pylab option, so I don't need
> to use show(). My question is, how do I maintain a *constant* xlabel and
> ylabel without having to redraw them each time I append a point to the
> graph? If I try xlabel('something') then obviously it's cleared each
> time I use plot(X,Y).

I'm not sure I understand well, but if one uses xlabel("something") before the 
while-loop or just after building the figure, it is not redrawn after 
plotting.

regards
Matthias

Re: [Matplotlib-users] Labels in a dynamic graph

[John H. <jd...@gm...>]

On Sun, Mar 23, 2008 at 3:54 AM, Amit Finkler <ami...@gm...> wrote:

> I am using matplotlib to dynamically plot a graph with both my x and y
> points taken from a measurement device. That is to say, in each iteration of
> my while loop I'm reading two variables which I then want to plot with
> matplotlib.

You will want to do something like (this is just a sketch)

xdata = []
ydata = []

fig = figure()
ax = fig.add_subplot(111)
ax.set_xlabel('my xlabel')
ax.set_ylabel('my ylabel')
line, = ax.plot(xdata, ydata)

def add_point(x, y):
    xdata.append(x)
    ydata.append(y)
    if len(xdata)>30:  # optional, prune the early points
        del xdata[0]
        del ydata[0]
    xmin = xdata[0]
    xmax = xdata[-1]
    line.set_data(xdata, ydata)
    ax.set_xlim(xmin, xmax)
    fig.canvas.draw()

while 1:
    x,y = get_data_point()
    add_point(x, y)

JDH

Re: [Matplotlib-users] Labels in a dynamic graph

[Amit F. <ami...@gm...>]

John Hunter wrote:
> On Sun, Mar 23, 2008 at 3:54 AM, Amit Finkler <ami...@gm...> wrote:
>
>   
>> I am using matplotlib to dynamically plot a graph with both my x and y
>> points taken from a measurement device. That is to say, in each iteration of
>> my while loop I'm reading two variables which I then want to plot with
>> matplotlib.
>>     
>
> You will want to do something like (this is just a sketch)
>
> xdata = []
> ydata = []
>
> fig = figure()
> ax = fig.add_subplot(111)
> ax.set_xlabel('my xlabel')
> ax.set_ylabel('my ylabel')
> line, = ax.plot(xdata, ydata)
>
> def add_point(x, y):
>     xdata.append(x)
>     ydata.append(y)
>     if len(xdata)>30:  # optional, prune the early points
>         del xdata[0]
>         del ydata[0]
>     xmin = xdata[0]
>     xmax = xdata[-1]
>     line.set_data(xdata, ydata)
>     ax.set_xlim(xmin, xmax)
>     fig.canvas.draw()
>
> while 1:
>     x,y = get_data_point()
>     add_point(x, y)
>
> JDH
>   
John,

Thanks for getting back to me. Indeed this works, at least when I try it
line by line. When I inserted it into my module, it shot back some error
message which goes like this:

      File
    "/usr/lib/python2.4/site-packages/matplotlib/backends/backend_tkagg.py",
    line 154, in draw
        FigureCanvasAgg.draw(self)
      File
    "/usr/lib/python2.4/site-packages/matplotlib/backends/backend_agg.py",
    line 392, in draw
        self.figure.draw(renderer)
      File "/usr/lib/python2.4/site-packages/matplotlib/figure.py", line
    544, in draw
        for a in self.axes: a.draw(renderer)
      File "/usr/lib/python2.4/site-packages/matplotlib/axes.py", line
    1004, in draw
        try: self.transData.freeze()  # eval the lazy objects
    ValueError: Domain error on eval_scalars in Transformation::freeze

Since it did work on the console, i.e., line by line, I think it's only
a matter of resolving my own source code, unless of course you think
otherwise. By the way, isn't there a way to do the set_xlim/ylim
automatically? When I use only figure(), hold(False) and plot(X, Y), it
updates it automatically, so why doesn't it do it with the subplot?

Thanks for your help.

Amit.

Re: [Matplotlib-users] Labels in a dynamic graph

[John H. <jd...@gm...>]

On Tue, Mar 25, 2008 at 11:39 AM, Amit Finkler <ami...@gm...> wrote:

>  I am using matplotlib to dynamically plot a graph with both my x and y
> points taken from a measurement device. That is to say, in each iteration of
> my while loop I'm reading two variables which I then want to plot with
> matplotlib.

Odd, are you using an older version of matplotlib (it works for me).
Try seeding your data with an initial point

xdata = [x]
ydata = [y]

or setting the axis limits before plotting

ax.set_xlim(0,1)
ax.set_ylim(0,1)

Not sure why you are having problems....

JDH