Speed differences in sym and vpa

I am working on an optimization problem that involves calling the Symbolic Math toolbox. The sym function makes optimization very slow, so I tried vpa and it made it a lot faster. I am wondering where the speed difference comes from? Is it the fact that sym converts everything to rational form while vpa doesn't? If so, should sym(x,'d') do the same thing as vpa(x) because now they're in the same form?

Thanks!

Answer 1

[Walter Roberson]

vpa() switches to arithmetic calculations with the default number of digits (unless you asked for different). That can be a lot faster than trying to find symbolic equivalences and symbolic special cases -- and is likely to require far fewer terms.

[Pat]

Thanks for your answer. Does this mean that sym(x,'d') is the same as vpa(x)?

Answer 2

[Alan Weiss]

I recommend using matlabFunction for optimizing symbolic variables and functions. There is an extensive example here, and another example here.

Alan Weiss

MATLAB mathematical toolbox documentation