How to solve NaN error, while dealing with multiplication of double values

Question

i am getting NaN error in the program.
consider this following code
for (j=0;j<nh;j++)
sum = 0.0;
for (i=0;i<ni;i++){ sum = sum + (ai[i] * wi[i][j]) ;}
//System.out.println(sum);
ah[j] = sigmoid(sum);
public static float sigmoid(float x)
return ((Math.exp(x)- Math.exp(-x)) / (Math.exp(x)+Math.exp(-x)));
ni = 2500-- no of input nodes;
nh = 5000 -- no of hidden nodes;
i am getting problem in calculating the "sum" value. its returning NaN for "sum".
here a[i] values are around some +/- 0.XXXXXXXX upto 14 digits
and wi[j][j] values are also +/- 0.XXXXXX upto 14 digits.
all values are of datatype double.
i was stucked up with this problem. what i am to do?
give me suggestions..
please reply me

Answer 1

This can occur with double divisions. I wrote a small method that solves this:
     * Set double values that have a value of 'NaN' or 'Infinity' to 0.0. This can happen when dividing double values as they
     * don't cause a DivisionByZeroException.
     * @param value Double value to check.
     * @return Input value with 'NaN' and 'Infinity' set to 0.0.
    static public double resetNaN(final double value, final double resetValue) {
        return (Double.isNaN(value) || Double.isInfinite(value)) ? resetValue : value;
    }//resetNaN()