Confusion Concerning Numerical Equation

[drug]

16.11.2019 13:01, Avery Stupidman пишет:
> Hello,
> 
> I have a function "angle" that returns the angle (in degrees) of a right 
> triangle given the length of the its lengths as type "real". It works, 
> but when trying to test the equality of the angle with the seemingly 
> identical value, I'm informed that the two are not equal. Thus, when 
> angleDeg(sqrt(3.0)/2.0, 1.5) returns 60, the comparison 
> "angleDeg(sqrt(3.0)/2.0, 1.5) == 60" resolves to false.
> 
> I'm most likely stupid and sleep deprived, but if I may have some 
> elucidation, I'd be very grateful.
> 
> Some code:
> 
> real angleDeg(real x, real y)
> {
>      import std.math : PI, abs, atan2, sgn;
> 
>      auto angle = atan2(y, x);
> 
>      // Simplify angle if vector resides in quadrants II or III
>      if (x < 0)
>      {
>          angle = (PI - abs(angle)) * sgn(angle);
>      }
> 
>      return angle * 180 / PI;
> }
> 
> import std.math : sqrt;
> 
> assert(angleDeg(sqrt(3.0)/2.0, 1.5) == 60.0); // Fails
In general you shouldn't compare floating point values for equality 
because of their nature, you can use something like approxEqual 
https://dlang.org/library/std/math/approx_equal.html

P.S. see also https://floating-point-gui.de/errors/comparison/