[Cuis-dev] testing Float results

[Martin McClure]

Hi Mark,

Welcome to the list -- good to see you diving into Cuis!

As Andres says, there are messages to do this kind of test on Floats.

I find myself compelled, however, to warn about using such 
"approximately equal" tests when inappropriate. I recently discovered 
this kind of usage in an ancient test framework, and it was allowing 
tests to pass that should not have. Those tests are being replaced with 
equality tests.

As I commented to a co-worker just this morning, accepting as correct a 
Float result that is one ULP different from the correct Float is really 
no different than accepting 5 as a correct answer to 2 + 2.

There are, of course, times when figuring out the exact rounding 
expected in a sequence of floating-point operations is impractical, and 
accepting a certain amount of cumulative error is OK. Floats are often 
used in applications where accuracy is only required to some specific 
precision, but it's also good to keep in mind that each Float precisely 
represents one value, and each operation on a Float has only one correct 
answer.

Regards,
-Martin

On 6/3/24 19:49, Andres Valloud via Cuis-dev wrote:
> Look at Float>>isWithin:floatsFrom:, and see also Float>>ulp.
>
> On 6/3/24 4:36 PM, Mark Volkmann via Cuis-dev wrote:
>> Is there a function that tests whether two Float values are "close" 
>> (within some delta)?
>> I can write it, but I thought that might be provided.
>> I looked at all the methods in the Float class, but didn't find one 
>> like that.
>>
>> -- 
>> R. Mark Volkmann
>> Object Computing, Inc.
>>