Re: String-to-Number Conversion Precision

*To*: mathgroup at smc.vnet.net*Subject*: [mg112381] Re: String-to-Number Conversion Precision*From*: Ben <benp84 at gmail.com>*Date*: Sat, 11 Sep 2010 05:46:23 -0400 (EDT)*References*: <i6crfo$sa1$1@smc.vnet.net> <i6d0cn$1l5$1@smc.vnet.net>

On Sep 10, 4:13 am, Peter Breitfeld <ph... at t-online.de> wrote: > Ben wrote: > > I'm reading real numbers from a file and I'm trying to convert them > > from string format (with arbitrary precision) to real values with the > > same precision as given in the strings. > > > For example, when I convert "1.867524468", I want the result to be set > > to precision 10. Instead, I get the following. > > > In[1]:= string = "1.867524468" > > Out[1]:= "1.867524468" > > > In[2]:= x = ToExpression[string] > > Out[2]:= 1.86752 > > > The last 4-digits get cut off. This is fine for when I do math with > > the number because the extra digits are still stored, but not when I > > want to rewrite the number to a different file. When I convert the > > number back to a string for file output, the last 4-digits remain > > lost. > > > In[3]:= ToString[x] > > Out[3]:= "1.86752" > > > Is there a function or formula I can use to automatically set the > > precision of these numbers to their precision in the string? Thanks. > > Mathematica treats numbers with less then $MachinePrecision digits > always as having MachinePrecision. It _displays_ them with 6 digits > after the decimal point, but knows all the digits. You can display them > using NumberForm or better (in this case) using InputForm. So > > In[3]:= ToString[InputForm[x]] > > will give you all the original digits. > > To set the precision for longer numbers according to the length of the > input string you may use something like this: > > string = "1.867524468121212771299123312"; > x = ToExpression[string] > SetPrecision[x, StringLength[string] - 1] > {Precision[x], Accuracy[x]} > InputForm[x] > > -- > _________________________________________________________________ > Peter Breitfeld, Bad Saulgau, Germany --http://www.pBreitfeld.de That'll work. Thank you!