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Any idea to convert numerics to symbolic ?

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Stephan Moeller
Stephan Moeller 2014-6-2
关闭： MATLAB Answer Bot 2021-8-20
How can I convert an equation with the numeric coeffs to symbolic ?
example :
y= 2*exp(3*x)+log10(4*x+9)+10
so I get
y= a1*exp(a2*x)+log10(a3*x+a4)+a5

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回答（4 个）

Andreas Goser
Andreas Goser 2014-6-2
I can think of string operations. But you need to find rules how to smartly cover situations where you don't want to replace a number with a variable like in x.^2.
Stephan Moeller
Stephan Moeller 2014-6-2
yes, me too. But there isn't anything already available as a function ?
  2 个评论
Andreas Goser
Andreas Goser 2014-6-2
Don't think so. I never heard of such an operation. Instead of numerics to symbolic I would also rather call it "generalizing coefficients" or so. But exactly because if this difficulty to name it, it is also difficult to search for it. Lets see if more people reply.
pietro
pietro 2014-6-2
You can use the symbolic toolbox. Here an example:
syms z,x
z=3*x; y=subs(z1,{3},{a})
With a workaround I think you can do what you need
  2 个评论
Stephan Moeller
Stephan Moeller 2014-6-2
I meant without explizit writing all numerics maunally.
pietro
pietro 2014-6-2
编辑：pietro 2014-6-2
you can write your formula in symbolic way, then using symvar you can get the symboli variables:
y=2*exp(3*x)+log10(4*x+9)+10 Then with symvar you can get the variables.
symvar(y)
ans =
x
so you can get everything since operators and functions are known. After having got the numeric values, you can substitute them using subs
Hope this helps
Andrei Bobrov
Andrei Bobrov 2014-6-2
编辑：Andrei Bobrov 2014-6-2
x= 'a':'z';
z = '2*exp(3*x)+log10(4*x+9)+10';
dd = regexp(z,'(?<=[\(-*/+ ])\d*|\d*(?=[+*-/\)])','match');
out = regexprep(z,dd',cellstr(x(1:numel(dd))'));

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