How to convert symbolic piecewise expression into a function handle
9 views (last 30 days)
Show older comments
I require to convert a symbolic piecewise expression to a function handle in matlab.
I tried using matlabFunction() but it throws a symengine error of unbalanced or unexpected parenthesis or bracket.
Any help will be highly appreciated.
6 Comments
Walter Roberson
on 26 Mar 2016
Edited: Walter Roberson
on 26 Mar 2016
There is no piecewise if you add the assumption that T >= 300
I recommend you use a different name for the upper bound, such as
syms Tmax
assume(Tmax>300)
fun = int(exp(-E/(8.314*T)),T,300,Tmax);
Now by the time you get to error1, you have a function in which both z and v are free variables. Is it correct that you are trying to minimize over both variables simultaneously?
Answers (1)
Walter Roberson
on 27 Mar 2016
If you write it out with the final integration step not done, and you expand() the terms and combine exponents and simplify, you can show that the minimum must occur when z is the mean of the alphaexp.
Near v = 0 and E = 18000, the integrals are very steep. The key point is near v = 0.002486920643673647643722704 where just a hair less gets you an integral that is so large that it effectively cannot be computed, but a hair more gets you an integral that is amazingly small -- for example values on the order of 1/10^(10^13). I think it means that the minimum is going to be at your upper bound, v < 6000 but the difference between that and any v > 0.002486920643673647643722704 would need to be computed to billions of digits to determine the difference. The inherent inaccuracy in your constants such as 8.314 do not justify those kinds of computations.
4 Comments
Walter Roberson
on 6 Apr 2016
Please do not name a variable "error" as that interferes with using the critical MATLAB function error() and makes it difficult for other people to read the code.
Please show the output of error1 and also the output of the matlabFunction call.
I have a vague memory that there might be a bug in the conversion of int() to function handle.
See Also
Categories
Find more on Assumptions in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!