Re: Re[2]: Exponential

[Douglas Handy <dhandy1@xxxxxxxxxxxxx>]

Patrick,

>it bothers me that 10**0 doesn't equal one in a
>nested expression.

Such is the nature of floating point.  It equaled 0.9999999... which
is why Ken suggested using %dech() to immediately round the nested
expression intermediate value.

>As a rule of thumb should I half round all eval statements?

As a rule of thumb, I try to avoid floating-point when practical,
especially with monetary values.  Then, when I do use floating-point,
I use half-adjust to help compensate for floating-point's inherent
inability to represent some numbers exactly.

As another rule of thumb, instead of just putting the half adjust on
the entire eval statement, I'd attempt deal with it immediately and
get the intermediate result back into a packed decimal format.

This can be done by using an extra EVAL(H) with just the
floating-ponit expression and a packed decimal result, or by judicious
use of %dech() such as in Ken's example.  But as Ken's example points
out, you need to understand the limits of your data such as only using
a positive exponent, etc.

In most cases, just using eval(h) may produce the same results.  But I
prefer to do the rounding at the intermediate result level with
floating-point, to avoid any potential of propagating and magnifying
the small discrepency in complex expressions.  Remember, if any
operand in an expression is floating-point, the operations are done in
floating point.  By using %dech() or a separate eval(h), the rest of
the expression will have only decimal operands and therefore can use
decimal arithmetic instead of floating-point.

Doug
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