IPython notebook interactive function: how to save the updated function parameters

Question

I wrote the code below in Ipython notebook to generate a sigmoid function controlled by parameters a which defines the position of the sigmoid center, and b which defines its width:

%matplotlib inline
    import numpy as np
    import matplotlib.pyplot as plt

def sigmoid(x,a,b):
    #sigmoid function with parameters a = center; b = width
    s= 1/(1+np.exp(-(x-a)/b))
    return 100.0*(s-min(s))/(max(s)-min(s)) # normalize sigmoid to 0-100

x = np.linspace(0,10,256)
sigm = sigmoid(x, a=5, b=1)
fig = plt.figure(figsize=(24,6))
ax1 = fig.add_subplot(2, 1, 1)
ax1.set_xticks([])
ax1.set_xticks([])
plt.plot(x,sigm,lw=2,color='black')
plt.xlim(x.min(), x.max())

I wanted to add interactivity for parameters a and b so I re-wrote the function as below:

%matplotlib inline
import numpy as np
import matplotlib.pyplot as plt
from IPython.html.widgets import interactive
from IPython.display import display

def sigmoid_demo(a=5,b=1):
    x = np.linspace(0,10,256)
    s = 1/(1+np.exp(-(x-a)/(b+0.1))) # +0.1 to avoid dividing by 0
    sn = 100.0*(s-min(s))/(max(s)-min(s)) # normalize sigmoid to 0-100
    fig = plt.figure(figsize=(24,6))
    ax1 = fig.add_subplot(2, 1, 1)
    ax1.set_xticks([])
    ax1.set_yticks([])
    plt.plot(x,sn,lw=2,color='black')
    plt.xlim(x.min(), x.max())

w=widgets.interactive(sigmoid_demo,a=5,b=1)
display(w)

Is it possible to save the modified sigmoid function parameters a and b to variables dynamically as they are modified by the sliders, so they can be used in another subplot or separate plot, and do further calculations.?

I've gone through all examples of interactive widgets I could find but have not see anything pointing in that direction (these widgets are fairly new, so documentation for them does not seem as extensive as for other features). Any suggestions in the right direction is appreciated.

Answer 1

You want to create the float widget manually:

from IPython.html.widgets import FloatSlider

# same as before

F1 = FloatSlider(value=5, min=0, max=10)
w=interactive(sigmoid_demo, a=F1, b=7)
display(w)

Then you can access F1.value any time after and it will be the current slider value.

You can also loop through w.widgets but that's painful.