# Unit Step Activation Function

Using the unit step activation function for the artificial neuron, determine a set of weights (and threshold value) that will produce the following classification:

x1  x2  output
-0.2 0.5    0
0.2 -0.5    0
0.8 -0.8    1
0.8 0.8     1


I understand the theory of unit step activation function (maybe beginner) but i am stumped as to how to calculate the weights and threshold values. I thought that it is specific to the problem and is provided as input. Please help

• Welcome to DataScience.SE! Is this a homework question? – Emre May 5 '16 at 6:07
• Thanks!. Yes. I am taking an online class but the support is very minimal. Its ok if you can give a few tips that will help me solve this question – Trupti Dongargaonkar May 7 '16 at 2:15

Here is what i did. Not sure if this is correct. Will have update next week.

I plotted these 4 points on a graph with x1 and x2 on x and y axis respectively. since its a unit step function, which essentially has 1 or 0 output - i tried to draw a linear regression line such that all "0" result points are on 1 side and "1" result points are on other. This gave me the possible weights w1 and w2 and i constructed an equation

w1= 1.5 and w2 = 0.5

Then i made a table to check if the equation provided the actual results

i started adjusting the w1 and w2 to try to "fit" to training data but one data was just not working!!

i could bring the error down at w1=1 and w2 =0.39

Then - the threshold value, T it should be in such a way that the z = x1w1+x2w2 + T and y=0 if z<0 and y=1 if z<=0. The value of T should change the results of (0.2,-0.5 ) to fit but not change the result of other points. So i started at -0.4 and worked my way up to -0.44.

Final equation came out to be. y = x1 + 0.39x2 -0.44

This fits the current training data.