## STD-PROPOSALS | |

**Subject:** Re: [std-proposals] new approximately equal operators

**From:** Vishal Oza (*vickoza_at_[hidden]*)

**Date:** 2020-06-08 17:25:37

**Next message:**Bjorn Reese: "Re: [std-proposals] new approximately equal operators"**Previous message:**Nikolay Mihaylov: "Re: [std-proposals] new approximately equal operators"**In reply to:**Nikolay Mihaylov: "Re: [std-proposals] new approximately equal operators"**Next in thread:**Jake Arkinstall: "Re: [std-proposals] new approximately equal operators"**Reply:**Jake Arkinstall: "Re: [std-proposals] new approximately equal operators"**Reply:**Michael Hava: "Re: [std-proposals] new approximately equal operators"

for you questions

1. epsilon would be a very small number close to zero but not zero.

Having epsilon as a variable might not be needed in there is a way to track

the accuracy of floating point error over the course of the calculation to

the operator.or we might be about to use the exponent to compute what

epsilon value seem reasonable

2. yes it can be but it is extra pointless work the only reason I use

abs(a-b) is to remove the sign is the number is negative. It might also

this to work with complex number but I this I would have to explore this

further.

3. assignment of ~= does not compile in current C++ but in what I

propose a ~= 5000(0.1) would translate to abs(a-5000) < 0.1

also the == would be very unreadable according to your logic.

int f = 5000;

float x = 0.1;

auto a == f(x);

then what about:

int caruso(int a);

auto a == caruzo(f)(x);

or...

auto a == ( caruzo(f) )(x);

On Mon, Jun 8, 2020 at 3:06 PM Nikolay Mihaylov <nmmm_at_[hidden]> wrote:

> 1. What is epsilon?

> 2. didn't this abs(a-b) be abs(abs(a)-abs(b))

> 3. a ~=b(c) - b(c) this actually will be:

>

> auto a ~= 5000(0.1);

>

> is very unreadable.

> int f = 5000;

> float x = 0.1;

> auto a ~= f(x);

>

> then what about:

>

> int caruso(int a);

>

> auto a ~= caruzo(f)(x);

> or...

> auto a ~= ( caruzo(f) )(x);

>

>

>

>

> On Mon, Jun 8, 2020 at 10:55 PM Vishal Oza via Std-Proposals <

> std-proposals_at_[hidden]> wrote:

>

>> I was wondering if there is any interest in adding approximately equal to

>> operators into the language. The main purpose is to compare floating point

>> calculations with rounding error, however they could be used for similarity

>> of objects or fixed point rounded values as well.

>>

>> the operator I propose are: ~=, ~< , ~>, ~!

>> these operators would translate at least to floating point as

>> a ~= b ==> abs(a-b) < epsilon

>> a ~< b ==> (a < b) || (abs(a-b) < epsilon)

>> a ~> b ==> (a > b) || (abs(a-b) < epsilon)

>> a ~! b ==> abs(a-b) >= epsilon

>>

>> There are two routes I can see with default implementation this language

>> feature. either adding a default epsilon into the language that can be set

>> as a global variable or adding some way of tracking errors. I would like

>> more feedback on either way of default implementation.

>>

>> I would also like a way to specify the epsilon value or function for a

>> single comparison. the best I can think of is

>> a ~=b(c) ==> abs(a-b) < c

>> a ~=b:c ==> abs(a-b) < c

>> [c]a ~=b ==> abs(a-b) < c

>>

>> The precedence should be on the same level of all of the current

>> comparison operators.

>>

>> This could be introduced in C++ 23 or later in there is any interate.

>>

>> Sincerely,

>> Vishal Oza

>> --

>> Std-Proposals mailing list

>> Std-Proposals_at_[hidden]

>> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals

>>

>

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**Next message:**Bjorn Reese: "Re: [std-proposals] new approximately equal operators"**Previous message:**Nikolay Mihaylov: "Re: [std-proposals] new approximately equal operators"**In reply to:**Nikolay Mihaylov: "Re: [std-proposals] new approximately equal operators"**Next in thread:**Jake Arkinstall: "Re: [std-proposals] new approximately equal operators"**Reply:**Jake Arkinstall: "Re: [std-proposals] new approximately equal operators"**Reply:**Michael Hava: "Re: [std-proposals] new approximately equal operators"

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