problem in understanding the code

Question

i = 0;
while (fscanf(fp, "%f %f %d", &x[i], &y[i], &outputs[i]) != EOF) {
    if (outputs[i] == 0) {
        outputs[i] = -1;
    }
    i++;
}
patternCount = i;

I dont understand the meaning of this line from the above code:

if (outputs[i] == 0) {
        outputs[i] = -1;

What does it represent. The Output is a matrix or vector.??

The refrence of the code is: Perceptron learning algorithm not converging to 0

I have a output file that has 3 columns:

1 0 0
0 0 1
0 1 0

So it a vector file??

I don't understand how Matlab and C++ can be in the same question.... — Billy ONeal, Aug 11 '10 at 01:30
It is a `1-D` array, which is like a vector in math. It changes `v_i` where `v` is the vector and `i` is the index. — Hamish Grubijan, Aug 11 '10 at 01:32

score 3 · Accepted Answer · answered Aug 11 '10 at 03:24

outputs is defined as a one-dimensional array containing integer values..

float x[208], y[208];
int outputs[208];

Each index in the array can be seen as corresponding to a line read in the data file.

  i       x              y      outputs
  --------------------------------------
  0 | -8.818681   3.025210     1
  1 |  3.653846  -2.969188     0
  2 |  ...           ...           .
 .. |  ...           ...           .
208 | -6.565934  -4.649860     1

Where if i == 0 then

x[0]       == -8.818681
y[0]       == 3.025210
outputs[0] == 1

The wonderful code and information posted by user Amro explain the limits and function of outputs.

"...bias term, i.e. a third weight component connected to an input of value 1. (+1/-1) "

Values for outputs in the data file have been assigned one/zero values. Therefore the code in question checks to see if the value for outputs read in from the file is equal to zero and re-assigns to a -1.

if (outputs[i] == 0)
    outputs[i] = -1;

http://stackoverflow.com/questions/3454794/matlab-programming-for-perceptron---vcan u help me in this question too — user414981, Aug 11 '10 at 04:05
I would like to help, but I don't know anything about Matlab. — Adam, Aug 11 '10 at 19:46

score 2 · Answer 2 · answered Aug 11 '10 at 01:45

as far as I can tell, the code is reading from a file, and the file is supposed to have a repeated pattern, each pattern consists of 3 numbers.

Your loop copy the first number in each pattern to x, the second to y, and the last to outputs. However whenever the third number is a zero, it is changed to -1.

patternCount will store the number of pattern read in the file

paxdiablo · Answer 3 · 2010-08-11T02:16:37.307

2

A perceptron is a term from artificial intelligence/neural networks. It operates in much the same way as a single neuron is supposed to operate in the brain.

It has a number of inputs and a single output.

All this file is doing is specifying what the output should be for a given set of inputs. That's why the x/y and output are named differently.

As to why it's morphing the output from 0 to -1 (that's all it's doing by the way: changing zeros in the third file column into negative one), I'm not sure. The outputs of perceptrons almost invariably feed into other perceptrons so passing a -1 to something that expects 0 or 1 is an ... interesting ... idea.

edited Aug 11 '10 at 02:16

answered Aug 11 '10 at 01:56

paxdiablo

854,327
234
1,573
1,953

thanks....can u see my other question that I posted now...I need help in that question very badly. – user414981 Aug 11 '10 at 02:05
I'd love to help out, @ishamahajan, but I don't know Matlab unfortunately. – paxdiablo Aug 11 '10 at 02:18

problem in understanding the code

3 Answers3