Re: approximation
- To: mathgroup at smc.vnet.net
- Subject: [mg79469] Re: approximation
- From: chuck009 <dmilioto at comcast.com>
- Date: Fri, 27 Jul 2007 05:56:57 -0400 (EDT)
Just evaluate a to a particular level of precision with the N directive:
In[62]:=
a=1.56068376362920545943;
Print["The value is: ",N[a,2]]
Print["The value is: ",N[a,17]]
>From In[62]:=
The value is: 1.6
>From In[62]:=
The value is: 1.5606837636292055
Note the precision is as you entered it:
In[65]:=
Precision[a]
Out[65]=
20.1933
Now if you do anything with that number using a number less than that precision, the overall precision drops down to the lowest precision:
b=2.55
Precision[b]
Out[67]=
MachinePrecision
which is about 15 digits. You can see them with this command:
RealDigits[b]
Out[69]=
{{2,5,5,0,0,0,0,0,0,0,0,0,0,0,0,0},1}
Now, when I multiply them both, the overall precision drops down to 15:
net=a b;
Precision[net]
Out[71]=
MachinePrecision
Unless I explicitly set the precsion of 2.5 to say 21:
In[82]:=
b=SetPrecision[2.5,21]
net=a b;
Precision[net]
Out[82]=
2.50000000000000000000
Out[84]=
20.1303