Andrew Martin <mr.a.martin at gmail.com> writes:
> I have an expression including log().
>
> 2*(1/2 - log(2)/2);
>
> How can I make maxima evaluate the expression (hence returning approx 0.307)?
>
> I've looked at the log simplification flags, simp and ev, but they
> don't seem to have the effect I want.
>
> Cheers,
>
> Andrew
You need to tell Maxima that you want a floating point number. After
all, if you want to keep the exact "log(2)" in the answer, then 1-log(2)
is as simple as it gets. To force floating point evaluation, use the
"float" function:
(%i1) 2*(1/2 - log(2)/2);
1 log(2)
(%o1) 2 (- - ------)
2 2
(%i2) float(%o1);
(%o2) .3068528194400547
Another option is to use the "numer" flag for the implicit "ev" on the
command line:
(%i6) %o1, numer;
(%o6) .3068528194400547
Oddly enough, there is also a "float" flag, but this doesn't do what you
want, just converting all ratios to floats:
(%i7) %o1, float;
(%o7) 2 (0.5 - 0.5 log(2))
Note that if the inside of the log call had not been an integer, "float"
would have behaved as expected:
(%i12) 2*(1/2 - log(2/3)/2), float;
(%o12) 1.405465108108164
This is because the float flag converted the 2/3 to 0.66..7 and then log
of a floating point argument is simplified to the relevant
number. Confusing!
I confess my approach with this sort of thing is to write "%, float"
then swear and write "%, numer" if necessary...
Rupert
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