Hello there,

I am trying to build a square matrix of the type Double, with the following code:

for( i = 0; i < weightVector.length; i++) 

      for( j =0; j< weightVector.length; j++) 

         {
             weightMatrix[i][j]= weightVector[i]* weightVector[j];
             if(i==j)                                                               weightMatrix[i][i] += 0.0001;  
        }

The problem is each time the vector "weightVector" has a very small value (e.g the multiplication of the values 1.190597027811988E-273 and -2.513498651481222E-273) it gives zero as an answer, but if i work this out with a calculator, it gives me the right answer. Can you tell me why my programme is approximating its answer to zero, please?

Multiplying at those magnitudes are putting you beyond the precision of double. Use BigDecimal instead.

double a = 1.190597027811988E-273;
double b = -2.513498651481222E-273;
System.out.println("double: "+(a*b));
// double: -0.0

BigDecimal c = new BigDecimal(a);
BigDecimal d = new BigDecimal(b);
System.out.println("BigDecimal: "+new DecimalFormat("0.#######E0").format(c.multiply(d)));
// BigDecimal: -2.992564E-546
commented: A great poster, always helpful +2

Was trying to figure that out for debee too Ezzaral! You are great!

Thanks for your help. I do really appreciate

Please, i was trying to figure out how you can declare an array with the BigDecimal class. Can you help with this please

BigDecimal[][] weightMatrix = new BigDecimal[4][4];
for (int i=0; i<weightMatrix.length; i++){
    for (int j=0; j<weightMatrix[i].length; j++){
        weightMatrix[i][j] = new BigDecimal(yourValue);
    }
}

Thank you very much, that's very kind of you.