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Unformatted text preview: do not speak of a unique NaN
value but of many possible NaN values. Note that an 1 in the output of
a program may or may not indicate a programming error, depending on the
context.
Addition and subtraction with 1 also make mathematical sense. In the
1
parallel resistance example, we see that 1 + R2 = 1. This is true even if
R2 also happens to be zero, because 1 + 1 = 1. We also have a + 1 = 1
and a ; 1 = ;1 for any nite value of a. But there is no way to make
sense of the expression 1 ; 1, which must therefore have a NaN value.
(These observations can be justi ed mathematically by considering addition
of limits. Suppose there are two sequences xk and yk both diverging to 1,
e.g. xk = 2k , yk = 2k, for k = 1 2 3 : : :. Clearly, the sequence xk + yk
must also diverge to 1. This justi es the expression 1 + 1 = 1. But it is
impossible to make a statement about the limit of xk ; yk , without knowing
23 more than the fact that they both diverge to 1, since the result depends on
which of ak or bk diverges faster to 1.)
Exercise 17 What...
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 Spring '09
 LIE

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