MATLAB symbolic definite integration error while taking symbolic function as input arguments

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Noah Tang
Noah Tang 2024-11-4，14:46
评论： Walter Roberson 2024-11-4，18:49
The code is
syms v T;
int(@(x) x*v, 0, T)
int(@(tau) tau*v, 0, T)
I expect the answers to be T^2*v/2 but the second definite integration incorrectly contains τ.

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Sameer
Sameer 2024-11-4，15:01
编辑：Sameer 2024-11-4，15:45
Hi @Noah Tang
In the code you have provided, you are trying to perform symbolic integration using anonymous functions, which isn't directly compatible with MATLAB's "symbolic math" capabilities.
Here's a revised version of your code:
syms v T x tau;
% First integral
integrand1 = x * v;
result1 = int(integrand1, x, 0, T);
% Second integral
integrand2 = tau * v;
result2 = int(integrand2, tau, 0, T);
disp('Result of the first integral:');
disp(result1);
disp('Result of the second integral:');
disp(result2);
Hope this helps!
  1 个评论
Noah Tang
Noah Tang 2024-11-4，15:13
Thanks for your quick response! I now understand the difference between a symbolic function, which can be used as an input argument for the int function, and an anonymous function that involves a symbolic expression. Thanks again!

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Walter Roberson
Walter Roberson 2024-11-4，18:44
syms a v T
disp(int(@(tau) tau*v, 0, T))
disp(int(@(tau) tau*a, 0, T))
Notice that in the first case, it integrated with respect to v and kept tau constant, but in the second case it integrated with respect to tau and kept a constant.
What is happening is the anonymous function is being automatically converted to a symbolic expression (not a symfun !), and then the symbolic expression is being integrated with respect to the default variable. The default variable happens to be different between [tau, v] and [tau, a]
It is arguably a bug. On the other hand, no behaviour is documented for int() of anonymous functions.

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