Artificial Neural Network: NaN from a calculation

Question

Hi everyone,
I'm programming a small pattern recognition neural network at the moment but have ran into a small snag. I'm recieving a NaN result from a calculation and I don't know why.
    void calculateOutput()
        double preSigmoidOutput = 0d;
        //Find pre sigmoid output
        Iterator connectionsIterator = connections.iterator();
        while (connectionsIterator.hasNext())
            Connection connection = (Connection) connectionsIterator.next();
            preSigmoidOutput += connection.weight * connection.entryNode.output;
        //Perform Squash
        output = 1 / (1 + Math.log(preSigmoidOutput));
    }I think the problem is occuring at the "output = " line. I've already set a breakpoint and watched what was going on and basically preSigmoidOutput is usually a very small but long number (e.g. 0.05543464575674564) which then at the line "output = " produces a NaN result. Is that mathematical operation overflowing the double datatype? And if so how would I got about stopping this?
Thanks,
Chris

Answer 1

tsith wrote:
sabre150 wrote:
BlueWrath wrote:
Turns out this line:
double logVal = Math.log(-preSigmoidOutput);Causes a NaN result even though preSigmoidOutput is a valid double (in the case i'm examining now preSigmoidOutput is equal to 0.01067537271542014). Anyone know why i'm getting a NaN result from this code?I hope the value of 'preSigmoidOutput' is less than zero since if it is zero the log() is -infinity and if positive then you are taking the log of a negative number which is illegal.Flag on the play! OP loses 10 yards:-) That will teach me to skip the rest of a post when I know what is wrong!