Avoid MachinePrecision numbers in Message

Question

Can I change the output of Message to not show MachinePrecision numbers? E.g.

Bleh::test = "test `1`";

This is tolerable:

Message[Bleh::test, 0.01]
(* Bleh::test -- test 0.01` *)

This is not:

xx = 0.01;
Do[xx += 0.04, {5}]
Message[Bleh::test, xx]
(* Bleh::test -- test 0.21000000000000002` *)

Is there a way for Message to display this rounded off as:

xx
(* 0.21 *)

Message[Bleh::test, ToString@xx] uses the current PrintPrecision, I think. -- Well, no, apparently not, but it rounds the output as desired. — Michael E2, Oct 13, 2020 at 1:39
@MichaelE2 I thought it might be simple. Want to add as an answer? — Chris K, Oct 13, 2020 at 1:43
I think NumberForm or StandardForm will work better than ToString. — Carl Woll, Oct 13, 2020 at 3:21

Michael E2 · Accepted Answer · 2020-10-13 01:44:14Z

4

ToString seems to round the output as is usually done in output cells (technically in OutputForm, which is not the same as the "Output" style):

xx = 0.01;
Do[xx += 0.04, {5}]
Message[Bleh::test, ToString@xx]

Bleh::test: test 0.21

answered Oct 13, 2020 at 1:44

Michael E2

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2

$\begingroup$ Single argument ToString uses OutputForm. If the number is a rational or needs scientific notation, the output will be very bad, e.g., xx=1/7; Do[xx += 1/16, {5}]; Message[Bleh::test, ToString@xx] $\endgroup$
– Carl Woll
Oct 13, 2020 at 3:18
$\begingroup$ @CarlWoll Quite. I took MachinePrecision to mean, well, MachinePrecision. $\endgroup$
– Michael E2
Oct 13, 2020 at 3:34
1

$\begingroup$ A rational example was simpler, but a scientific notation example is xx = 1.1*^6; Do[xx += 1.1*^7, {5}]; Message[Bleh::test, ToString@xx]. Basically, you should almost never use single argument ToString. $\endgroup$
– Carl Woll
Oct 13, 2020 at 3:47
$\begingroup$ @CarlWoll Thanks, I didn't think of that. $\endgroup$
– Michael E2
Oct 13, 2020 at 3:48
$\begingroup$ Thanks, this solved my problem, although @CarlWoll's suggestions of StandardForm or NumberForm might be more robust to non-MachinePrecision numbers. $\endgroup$
– Chris K
Oct 14, 2020 at 2:06

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