Marcio wrote:
> please, what if the symbolic equation is calculated like this?
> sum1=0;
> for i=1:n
> sum1 = sum1 + 1/(1V);
> end
> so, the coefficients of sum1 are going to appear in that large format,
> how can I use the "sym" command to convert it to a short number instead of a fraction?
It is not clear from your posting what V is. If V is a matlab number, or is
sym(a numeric constant), then double(sum1) will evaluate to the single
double precision floating point equivalent of sum1.
If, though, V is a symbolic name so your expression is some large expression
with a mix of fractions and operations and symbolic names and exponents,
and you want to reduce it that is a mix of simple fixedpoint numbers and
operations and symbolic names and exponents, then the pure Maple call to do
that would be evalf(sum1) which would use the default Digits setting for the
precision, or evalf(sum1, N) which would use N digits for the precision.
I do not know how you would invoke that Maple call from Matlab; possibly
vpa(sum1) or vpa(sum1,N) would be the equivalents.
Usually, though, it is better to keep the fraction form around as long
as possible, using simplification and factorization and collection to
make it more humanly readable when that is needed. Then when you want to
evaluate the expression with a specific numeric value in place of the
symbol, you would use the Maple call subs() or eval(). If the numeric value
being substituted is in decimal format, then subs() or eval() will
automatically collapse as much as possible down to a decimal number.
For example the Maple call
subs(V=1/3,1/2+V) would result in the symbolic fraction 5/6 but
subs(V=0.333,1/2+V) would result in the symbolic number 0.8330000000 
the decimal number triggers the collapse of all of the fractions.
But either way, you still need to double() these symbolic numbers to
get a double precision number that Matlab can operate on directly.
Sorry, I do not have the symbolic toolbox myself so I do not know what
the Matlab equivalent of all of the Maple forms are. I have Maple itself and
know it relatively well (the language itself, anyhow  the libraries are too
big for any one person to reasonably understand them all.)
