Trouble substituting a value into a symbolic expression for use with fplot

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Bob
Bob 2012-3-20
编辑： work wolf 2017-12-11
I'm having difficulty understanding what I'm doing wrong here:
syms x a
f=exp(x-a);
g=subs(f,'a',sym(0));
fplot(g,[-5 5])
I get the error:
Error using fcnchk (line 103)
If FUN is a MATLAB object, it must have an feval method.Error in fplot (line 61)
fun = fcnchk(fun);
If I explicitly define g as being a symbolic function:
fplot(@(x)g,[-5 5])
Undefined function 'isfinite' for input arguments of type 'sym'.
Error in fplot (line 113)
J = find(isfinite(y));
I clearly am not understanding the way the symbolic toolbox works and would appreciate a pointer.

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采纳的回答

Alexander
Alexander 2012-3-20
The command fplot only takes function handles, not symbolic objects. The easiest way to plot symbolic objects is using ezplot:
ezplot(g,[-5 5])
If you want to use fplot, you can use the command matlabFunction to convert the symbolic object into a MATLAB anonymous function:
fplot(matlabFunction(g),[-5 5])
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Walter Roberson
Walter Roberson 2017-12-11
fplot() does accept symbolic objects in modern versions, but did not when the question was originally asked.
work wolf
work wolf 2017-12-11
编辑：work wolf 2017-12-11
Dear, Walter Roberson. Thanks, I had problem about using symfun with fplot(). Thus, I used
matlabFunction(f)
instead of
symfun(formula,variables)
Please, see my Question here

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