## digitalmars.D - Unum rebuttal

- Walter Bright (5/5) Sep 14 https://people.eecs.berkeley.edu/~wkahan/UnumSORN.pdf
- Joseph (10/16) Sep 14 It's hard to know what's going on when there are mistakes in his
- Timon Gehr (6/21) Sep 15 No, he means what he wrote, which is
- Joseph (4/25) Sep 15 What are you saying? You haven't changed anything but slight
- Timon Gehr (10/44) Sep 16 I'm saying that there is no mistake in the expression you indicate nor
- mate (7/13) Sep 14 Prof. Gustafson refutes the critique on this one paper during a
- Timon Gehr (2/5) Sep 15 What about implicit precision-tampering? ;)
- Walter Bright (6/7) Sep 15 User error, do not pass Go, do not collect $200.
- Nick Barbalich (4/6) Sep 15 Walter

https://people.eecs.berkeley.edu/~wkahan/UnumSORN.pdf Prof Kahan, who pretty much invented IEEE 754 floating point arithmetic, debunks unums. Unums pop up now and then with "why don't we support them?" The bottom line is there is no magic solution to floating point problems. Unums just trade one set of problems for another.

Sep 14

On Friday, 15 September 2017 at 03:49:02 UTC, Walter Bright wrote:https://people.eecs.berkeley.edu/~wkahan/UnumSORN.pdf Prof Kahan, who pretty much invented IEEE 754 floating point arithmetic, debunks unums. Unums pop up now and then with "why don't we support them?" The bottom line is there is no magic solution to floating point problems. Unums just trade one set of problems for another.It's hard to know what's going on when there are mistakes in his examples that lead to wrong behavior. How can be be taken seriously if his rebuttle has basic mistakes and typos? https://people.eecs.berkeley.edu/~wkahan/EndErErs.pdf page 5: (y - sqrt(y^2 + 1)) - 1/(y + sqrt(y^2 + 1)) is not zero for all y. I assume he means (y - sqrt(y^2 + 1)) + 1/(y + sqrt(y^2 + 1))

Sep 14

On 15.09.2017 06:14, Joseph wrote:... How can be be taken seriously if his rebuttle has basic mistakes and typos?:-)https://people.eecs.berkeley.edu/~wkahan/EndErErs.pdf page 5: (y - sqrt(y^2 + 1)) - 1/(y + sqrt(y^2 + 1)) is not zero for all y. I assume he means at (y - sqrt(y^2 + 1)) + 1/(y + sqrt(y^2 + 1))No, he means what he wrote, which is |y-√(y²+1)| - 1/(y+√(y²+1)). In D notation: abs(y-sqrt(y^^2+1)) - 1/(y+sqrt(y^^2+1)).

Sep 15

On Saturday, 16 September 2017 at 02:27:23 UTC, Timon Gehr wrote:On 15.09.2017 06:14, Joseph wrote:What are you saying? You haven't changed anything but slight notational differences. It's still wrong, so if he really means that then he is wrong, else it's just you.... How can be be taken seriously if his rebuttle has basic mistakes and typos?:-)https://people.eecs.berkeley.edu/~wkahan/EndErErs.pdf page 5: (y - sqrt(y^2 + 1)) - 1/(y + sqrt(y^2 + 1)) is not zero for all y. I assume he means at (y - sqrt(y^2 + 1)) + 1/(y + sqrt(y^2 + 1))No, he means what he wrote, which is |y-√(y²+1)| - 1/(y+√(y²+1)). In D notation: abs(y-sqrt(y^^2+1)) - 1/(y+sqrt(y^^2+1)).

Sep 15

On 16.09.2017 05:32, Joseph wrote:On Saturday, 16 September 2017 at 02:27:23 UTC, Timon Gehr wrote:I'm saying that there is no mistake in the expression you indicate nor in the claims made about it.On 15.09.2017 06:14, Joseph wrote:What are you saying?... How can be be taken seriously if his rebuttle has basic mistakes and typos?:-)https://people.eecs.berkeley.edu/~wkahan/EndErErs.pdf page 5: (y - sqrt(y^2 + 1)) - 1/(y + sqrt(y^2 + 1)) is not zero for all y. I assume he means at (y - sqrt(y^2 + 1)) + 1/(y + sqrt(y^2 + 1))No, he means what he wrote, which is |y-√(y²+1)| - 1/(y+√(y²+1)). In D notation: abs(y-sqrt(y^^2+1)) - 1/(y+sqrt(y^^2+1)).You haven't changed anything but slight notational differences.The first expression you showed did not take the absolute value of the minuend. The second expression you showed also demonstrates rounding error, but it is not what he meant to write.It's still wrong,He says the function Q is zero for all positive arguments, which it is.so if he really means that then he is wrong, else it's just you.I'll go as far as to agree that one of the three of us is wrong. (Or let's make it four; the expression and a slightly weaker version of the claim also occur in Gustafson's book.)

Sep 16

On Friday, 15 September 2017 at 03:49:02 UTC, Walter Bright wrote:https://people.eecs.berkeley.edu/~wkahan/UnumSORN.pdf Prof Kahan, who pretty much invented IEEE 754 floating point arithmetic, debunks unums. Unums pop up now and then with "why don't we support them?" The bottom line is there is no magic solution to floating point problems. Unums just trade one set of problems for another.Prof. Gustafson refutes the critique on this one paper during a debate with Prof. Kahan: https://www.youtube.com/watch?v=LZAeZBVAzVw It seems to me unums are a nice design to make floating point computation accessible to more. It does not solve all problems, but it does not need to to improve the situation.

Sep 14

On 15.09.2017 05:49, Walter Bright wrote:The bottom line is there is no magic solution to floating point problems.What about implicit precision-tampering? ;)

Sep 15

On 9/15/2017 7:53 PM, Timon Gehr wrote:What about implicit precision-tampering? ;)User error, do not pass Go, do not collect $200. --- That reminds me, we do have a solution for the rounding issue: https://github.com/dlang/druntime/pull/1621 It's been drifting there for over a year.

Sep 15

On Friday, 15 September 2017 at 03:49:02 UTC, Walter Bright wrote:The bottom line is there is no magic solution to floating point problems. Unums just trade one set of problems for another.Walter so what do you see as the trade-offs as being ? Nick

Sep 15