strange output from ToExpression

Question

I want to set constraints to my parameters, e.g., "m", but Mma gives nonsensical output. How could I avoid this phenomenon by using another but "equivalent expression"? Or, is this just in my computer (i.e. a non-reproducible problem)?

case 1. output is as expected:

ToExpression[
 ToString[2.] <> ToString[">"] <> ToString["m"] <> ">=" <> 
  ToString[1.]]

2. > m >= 1.

case 2. output is unexpected:

ToExpression[
 ToString[0.10465923419974825] <> ToString[">"] <> ToString["m"] <> 
  ">=" <> ToString[-6.0857416503171394*^-6]]

-60.8574

The ToString[-6.0857416503171394*^-6] is problematic. (-6.08574 * 10 == -60.8574) Use Row[] or StringForm[]. — J. M.'s missing motivation, Apr 10 '13 at 12:42
But, maybe you'd like to use Inequality instead: (#1 > m >= #2) &[0.10465923419974825, -6.0857416503171394*^-6] — J. M.'s missing motivation, Apr 10 '13 at 12:51

score 3 · Answer 1 · answered Apr 10 '13 at 12:44

The documentation says:

ToString[expr] gives a string corresponding to the printed form of expr in OutputForm.

The problem is with the OutputForm string of the exponent in the number:

ToString[-6.0857416503171394*^-6]

           -6
-6.08574 10

You can specify InputForm in this conversion with the second argument of ToString:

ToExpression[
 ToString[0.10465923419974825] <> ">" <> "m" <> ">=" <> 
  ToString[-6.0857416503171394*^-6, InputForm]
]

0.104659 > m >= -6.08574*10^-6

Note that you do not need ToString around things that are explicitly Strings.

strange output from ToExpression

1 Answers1