Re: Why Mathematica does not issue a warning when the calculations

• To: mathgroup at smc.vnet.net
• Subject: [mg117697] Re: Why Mathematica does not issue a warning when the calculations
• From: Peter Pein <petsie at dordos.net>
• Date: Wed, 30 Mar 2011 04:09:06 -0500 (EST)
• References: <imfa3k\$iks\$1@smc.vnet.net> <imsh8t\$5lt\$1@smc.vnet.net>

```Am 29.03.2011 13:54, schrieb John Travolta Sardus:
...
> Just to make an (extreme?) example of what can happen, I was fooling
> around with ill-conditioned matrices, to see whether I could obtain
> accurate results for the solution of ill-conditioned linear systems
> using the second argument to the N function. After a while of playing
> around I entered the following (I wanted to introduce a new vector of
> known values into my calculations)
>
> b = {1, -999999999999998}
>
> Resulting into the output:
>
> {1, -999997999000002}
>
>
> I guess one needs first to learn how to use Mathematica, then he can use
> it effectively
>
>
>
>
>

As you entered (exact) integer values, it is hard to believe that any
version of Mathematica should have given the above result:

In[1]:= b = {1, -999999999999998}

Out[1]= {1, -999999999999998}

and even inexact input will not be altered in a visible way (if any):

In[2]:= b={1.,-999999999999998.}
Out[2]= {1.,-1.*10^15}
In[3]:= NumberForm[%,20]
Out[3]//NumberForm= {1.,-9.99999999999998*10^(14)}

what did you do to the poor (not so) small numbers?

sorry, I don't get it

```

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