I have an array called upperflatpoints, when I run the following code: echo("upperflatpoints",upperflatpoints); echo(upperflatpoints[1],upperflatpoints[2],upperflatpoints[1]==upperflatpoints[2],upperflatpoints[1][0]==upperflatpoints[2][0],upperflatpoints[1][1]==upperflatpoints[2][1],upperflatpoints[1].x==upperflatpoints[2].x,upperflatpoints[1].y==upperflatpoints[2].y); I get the following output in the Console: ECHO: "upperflatpoints", [[1.625, 1.625], [37.75, 1.625], [37.75, 1.625], [26, 1.625]] ECHO: [37.75, 1.625], [37.75, 1.625], false, true, false, true, false Notice the following in the output: 1. The values at index 1 & 2 have equal values 2. OpenSCad returns false when comparing [1] & [2] 3. When comparing the first value in each item, OpenSCad returns true, but when comparing the second value, OpenSCad returns false Why do the first & second values not return the same value? My ultimate goal is to test for equality between 2 points, but I cannot seem to find a way to do this when only part of the result is correct. Any ideas? Nathan Sokalski njsokalski@hotmail.com<mailto:njsokalski@hotmail.com>

1. The values at index 1 & 2 have equal values
2. OpenSCad returns false when comparing [1] & [2]
3. When comparing the first value in each item, OpenSCad returns true,
but when comparing the second value, OpenSCad returns false

Binary floating point numbers can't represent all decimal values exactly, so echo of values gets truncated/rounded to some extent. So values that appear the same from an echo do not always test the same for equality. I assume these values are coming from some kind of calculations. Unless the exact same operations are performed in the exact order with the same inputs, then they could be just a single least-significant-bit different which would fail an equality test. If you must do this sort of testing for same points from calculated values, I would checking that the distance between two points is below than some very small epsilon e.g: norm(p1 - p2) < 1e-6 On Tue, Mar 26, 2024 at 2:42 PM Nathan Sokalski via Discuss < discuss@lists.openscad.org> wrote: > I have an array called upperflatpoints, when I run the following code: > > echo("upperflatpoints",upperflatpoints); > > echo(upperflatpoints[1],upperflatpoints[2],upperflatpoints[1]==upperflatpoints[2],upperflatpoints[1][0]==upperflatpoints[2][0],upperflatpoints[1][1]==upperflatpoints[2][1],upperflatpoints[1].x==upperflatpoints[2].x,upperflatpoints[1].y==upperflatpoints[2].y); > > I get the following output in the Console: > > ECHO: "upperflatpoints", [[1.625, 1.625], [37.75, 1.625], [37.75, 1.625], > [26, 1.625]] > > ECHO: [37.75, 1.625], [37.75, 1.625], false, true, false, true, false > > Notice the following in the output: > > 1. The values at index 1 & 2 have equal values > 2. OpenSCad returns false when comparing [1] & [2] > 3. When comparing the first value in each item, OpenSCad returns true, > but when comparing the second value, OpenSCad returns false > > Why do the first & second values not return the same value? My ultimate > goal is to test for equality between 2 points, but I cannot seem to find a > way to do this when only part of the result is correct. Any ideas? > > > Nathan Sokalski > njsokalski@hotmail.com > _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email to discuss-leave@lists.openscad.org >

One good thing to try to diagnose this kind of thing is to subtract the two values, and echo the difference.  Thus, in this case, echo(upperflatpoints[1][1] - upperflatpoints[2][1]); Hans is probably right, that the two values are *almost* the same, but not quite.  This will show that clearly; probably the difference will be some number around 1e-15.