MATLAB vpa() doesn't compute variable-point number for expression with exponent?

Question

Trying to use vpa() to compute a variable point number for a rational expression in an exponent:

syms x;
ans1 = x^(12345/67890)
ans2 = vpa(x^(12345/67890),3)
ans2_5 = vpa((12345/67890),3)
ans3 = vpa(x*(12345/67890),3)

The above shows the issue. ans1 shows the default output of the expression. ans2 shows that vpa() is not computing the variable point number for the expression. ans 2_5 shows what it should be computing to. The result I'm looking for is x^0.182.

ans3 just shows that vpa() produces the expected result when the function is multiplication--it's something in the exponent that's tripping it up.

How can I request that the exponent be evaluated by vpa?

[edit]

Maybe I can make this more clear. All I really need is an accessor or index to the exponent of an exponential expression. So if my expression is y = x^a I need to be able to have some accessor on x that returns a.

Is this possible?

Answer 1

+1 for spotting this interesting bug. This solved your problem for me:

digits(3)
p=vpa(12345/67890,3)
ans1 = x^p

ans1 =
       x^0.182