Wrong result for a simple expression

[tomlux]

Hy,
I'm making this expression:
3.93 + 2.87 + 2.23 + 2.51 + 2.05 + 2+2.65 + 2.66 + 2.6 + 2.6 + 2.6 + 2.6 + 1.9 + 2.6 + 2.6

The result shoud be: 38.4

But I'm getting when running with the MathExpression as result: 38.400000000000006

Here the simple code:
MathExpression expression = new MathExpression("3.93+2.87+2.23+2.51+2.05+2+2.65+2.66+2.6+2.6+2.6+2.6+1.9+2.6+2.6"); System.out.println("expression.value = " + expression.evaluate().getValue());

Is this a bug in your library or what is here wrong?

Thanks,
Tom

[vatbub]

Hey Tom, the library saves number literals as doubles, the calculations are hence carried out using double precision. To me, this looks like usual rounding errors which occur when doing floating point calculations. I will have a closer look at it later today.

[vatbub]

I just tried your example and modified it a little:

MathExpression expression = new MathExpression("3.93+2.87+2.23+2.51+2.05+2+2.65+2.66+2.6+2.6+2.6+2.6+1.9+2.6+2.6");
double expected = 3.93 + 2.87 + 2.23 + 2.51 + 2.05 + 2 + 2.65 + 2.66 + 2.6 + 2.6 + 2.6 + 2.6 + 1.9 + 2.6 + 2.6;
Number result = expression.evaluate();
System.out.println("expression.value = " + result.getValue());
System.out.println("expected result: = " + expected);

I got the following console output:

expression.value = 38.400000000000006
expected result: = 38.400000000000006

This shows again that the issue is rounding related to floating point rounding errors. If you wish to read more about why this happens, you can read this overview on StackExchange or this paper if you wish to get more in-depth information.

Let me know if you need any other help with the library :)

[vatbub]

Apart from that, you may want to pull and run mvn install again as I just fixed issues #1 and #2 .
Cheers :)