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Topic: Symbolic expressions
Replies: 3   Last Post: Feb 20, 2013 9:26 AM

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 Steven Lord Posts: 18,038 Registered: 12/7/04
Re: Symbolic expressions
Posted: Feb 20, 2013 9:26 AM

"Christopher Creutzig" <Christopher.Creutzig@mathworks.com> wrote in message
news:5124D68E.6060500@mathworks.com...
> On 16.02.13 15:06, Shishir Jaiswal wrote:
>> I need to define a positive symbolic expression say 'n'.
>> I am using 'sym' or 'syms' (for multiple symbols). In one machine (PC) it
>> is working fine but in another following error is coming:

>
> Just a quick note: The difference between sym and syms is not whether
> you want a single or multiple symbols. It is true that syms can create
> multiple symbols at the same time, but the primary difference is that
> syms assigns the symbolic variable to the name given:
>

>>> sym x
>
> ans =
>
> x
>

>>> whos
> Name Size Bytes Class Attributes
>
> ans 1x1 112 sym
>

>>> syms x
>>> whos

> Name Size Bytes Class Attributes
>
> ans 1x1 112 sym
> x 1x1 112 sym
>
> Also, sym can handle expressions, while syms only defines variables and
> abstract functions. Note that entering expressions into sym is not
> really recommended, since the syntax is subtly different from MATLAB
> expressions.

One more big difference, and the reason I try always to use SYM instead of
SYMS when defining a symbolic variable inside a function, is that SYMS
"poofs" variables into the workspace. The SYM function, when called with an
output argument, does not.

function showpoof
peaks;
syms alpha
% The next line calls the ALPHA function. It does NOT attempt to index into
the variable with an index of 0.5
alpha(0.5)

beta = sym('beta');
% This next line does NOT call the BETA function.
beta(1, 1)

When you run this, you should see a translucent PEAKS surface (assuming you
have Symbolic Math Toolbox installed) and the variable beta should be
displayed in the Command Window.

--
Steve Lord
slord@mathworks.com