Find degree of non-polynomial expression in Matlab

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Hi,
say i have an expression as such:
syms x
y = x^(-5/2)
how to find the exponent of x since y is not a polynomial. is it possible?
thanks

Answers (2)

Star Strider
Star Strider on 15 Jul 2014
Unfortunately not.
In theory,
xpnt = log(y)/log(x)
should work because it’s a fundamental log identity for conversion between log bases. The Symbolic Math Toolbox simply returns the symbolic expression, not the exponent.
Maybe in a future release...

Christopher Creutzig
Christopher Creutzig on 29 Aug 2014
That depends on what exactly you are looking for in the general case. Here's something that works in this particular one:
>> simplify(log(y)/log(x),'IgnoreAnalyticConstraints',true)
ans =
-5/2
(The result is valid in general, but simplification succeeds along a way that ignores branch cuts and is not universally valid.)
If your expression gets more complicated, you may need to use MuPAD functions directly:
>> feval(symengine,'ldegree',feval(symengine,'series',y,x))
ans =
-5/2
(If you want to look at the output of the feval(symengine,'series',y,x) part, I heartily recommend the pretty function.

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