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Topic: Suitable form of solution
Replies: 6   Last Post: Feb 22, 2013 4:52 PM

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Steven Lord

Posts: 17,945
Registered: 12/7/04
Re: Suitable form of solution
Posted: Feb 22, 2013 4:52 PM
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"Milos Milenkovic" <m.milenkovic@mathworks.com> wrote in message
> As Stiven said solution is based on via VPA like in this case =>
> http://www.mathworks.com/matlabcentral/newsreader/view_thread/263694
> "Milos Milenkovic" <m.milenkovic@mathworks.com> wrote in message
> <kg85ib$eor$1@newscl01ah.mathworks.com>...

>> Please, look at this solution>


>> Why this has to be in fractional form and by what command specify the
>> solution of an equation in form of decimal numbers, or integer ..

Because Symbolic Math Toolbox prefers to keep the results of computations
exact, not approximating them by decimal, until or unless you tell it to
approximate using the DOUBLE function (to return the double precision
approximation) or the VPA function (to return the approximation to a certain
number of decimal places) on the result.

two = sym(2);
three = sym(3);
twothirds = two/three % fraction
twothirdsD = double(twothirds) % double approximation
twothirdsV = vpa(twothirds, 75) % approximation to 75 decimal places

4 - (twothirdsD+twothirdsD+twothirdsD+twothirdsD+twothirdsD+twothirdsD) %
not exactly 0
4 - (twothirds+twothirds+twothirds+twothirds+twothirds+twothirds) % exactly

Note that DOUBLE will not work if your symbolic expression contains a
variable that doesn't have a value, like (2/3)*t if t is not a variable. In
that case use VPA.

*more snip*

Steve Lord
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