MathNet Real number evaluation

Question

I have the following using MathNet library where child1 is -4.09 and child2 is -4.162. The result after Expression.Real((double1 - double2)) returns 0.072000000000000064. It should be 0.072. Can anyone please help me understand what is going on?

private static Expression GetSimplifiedExpression(Expression child1, Expression child2, LaTeXTokenType tokenType)
{
    double double1 = Evaluate.Evaluate(null, child1).RealValue;
    double double2 = Evaluate.Evaluate(null, child2).RealValue;

    return Expression.Real((double1 - double2));
}

This is how floating-point arithmetic works. There's a whole website devoted to explaining it: http://floating-point-gui.de/ — RBarryYoung, Jan 16 '18 at 20:44
you can use Decimal...thats a fixed point data type...not as flexible though — Ctznkane525, Jan 16 '18 at 22:20

Han Zhao · Answer 1 · 2018-01-17T07:22:11.120

First, let's convert decimal to binary:

-4.09 = -100.00010111000010100011110101110000101000111101011100001010001111...

-4.162 = -100.00101001011110001101010011111101111100111011011001000101101000...

Then, subtract those two binaries. The result in binary is:

0.00010010011011101001011110001101010011111101111100111011011001...

which is approximately equal to decimal 0.07199999999999999998.

It is not exactly 0.072000000000000064, but I think you could get the idea behind it. If you want the exact result, you could cast double to decimal:

var decimal1 = (decimal) double1;
var decimal2 = (decimal) double2;

MathNet Real number evaluation

1 Answers1