SetPrecision[]

*To*: mathgroup at yoda.ncsa.uiuc.edu*Subject*: SetPrecision[]*From*: uunet!yoda.ncsa.uiuc.edu!keiper%wri (Jerry Keiper)*Date*: Mon, 2 Apr 90 17:24:41 CDT

Jeffrey P. Golden <uiucuxc!ALLEGHENY.SCRC.Symbolics.COM!jpg> writes: >If the user types SetPrecision[1.2,30], I think it is pretty clear >that most users mean the same number that SetPrecision[12/10,30] >would mean, i.e. fill in with decimal 0's, which is not what >Mathematica does. Since that sort of functionality is in general impossible, I presume that the suggestion is only intended to make it more convenient to enter numbers precisely. But the 1.2 will have been converted to 1.001100110011... long before SetPrecision[] ever even gets to look at it. If the above functionality is desired one can do something like HighPrecision[x_, n_] := SetPrecision[Rationalize[x], n] then In[9]:= HighPrecision[1.2,40] Out[9]= 1.2 In[10]:= SetPrecision[%, 60] Out[10]= 1.19999999999999999999999999999999999999999999999917892668106 But this will only work for numbers that are essentially rational numbers with relatively small denominators with a small rounding error thrown in to allow it to be represented in binary. I do not think that overloading SetPrecision[] to have this functionality is appropriate. Jerry Keiper keiper at wri.com Wolfram Research Inc.