Table of functions for symbolic expressions

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Abdoulaye Thiam
Abdoulaye Thiam 2018-9-25
回答： Walter Roberson 2018-9-25
Hello,
I am asking how to declare a table of functions in Matlab for symbolic expressions.
The dimension of my table is n.
%Example : n=3
syms x
T(1) = x^2 ; T(2) = 2*x-1 ; T(3) = x^3 + 3 ;
Thank you

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Dimitris Kalogiros
Dimitris Kalogiros 2018-9-25
It is not exactly what you asked for, but I believe that it is close enough:
close all
clearvars
syms x n
f(x,n)=piecewise(n==1, 3*x-1, n==2, x^2-1, n==3, log(x))
Look, how it works:
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Abdoulaye Thiam
Abdoulaye Thiam 2018-9-25
I am iterating a process n times, each T(i) is a symbolic expression depending on x. Then T is close to a table. Let me look at your answer.
Thanks

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更多回答（1 个）

Walter Roberson
Walter Roberson 2018-9-25
You cannot create a sym array of functions: the entries stop being functions and become just expressions.
It is possible to create an array of symfun that all have the same arguments, but it is not possible to index into it: effectively what you get is a single symfun that returns a vector or array of results. To get around this you need to use cellfun
See also
https://www.mathworks.com/matlabcentral/answers/378731-how-to-solve-a-symbolic-system-of-first-order-linear-ordinary-differential-equation-using-ode15s-or#comment_614328
which shows additional problems if you try to create the function names dynamically.
For your purpose, I recommend creating an array of symbolic expressions (not functions!) and subs() the value of the argument into the function.
You can put symfun or sym into a table() object, with some care.

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