how to express operators in symbolic algebra
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I want to express an operator, P, which is simply the differential operator. I cannot find how to do this--one failed attempt is shown--any help appreciated
Fritz
==============================================
clear all
syms x
syms P(q), q(x)
q(x)=x^2
P(q) = diff(q(x),1) +5
return
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Réponses (3)
Walter Roberson
le 17 Déc 2023
MATLAB does not support creating operators: it only supports creating functions and expressions.
For example, P^3 to represent third derivative is not supported by MATLAB.
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Paul
le 17 Déc 2023
Modifié(e) : Paul
le 17 Déc 2023
I'm not sure how define a function of a function. But this seems to work, at least for this simple case:
syms x t
syms q(t) v(x) % v is our dummy function
P = diff(v,argnames(v),1) + 5 % "operator" P
q(t) = t^2
P(t) % show what P(t) is
subs(P(argnames(q)),v,q) % subs the dummy function with the actual function
Or, more generally w/o needing to know the symfun buried in P
subs(P(argnames(q)),symfun(findSymType(P,'symfun'),symvar(P)),q) % subs the dummy function
I'm not sure this is the best way.
It can probably be wrapped in cleaner functionality, like
operateon = @(P,q) subs(P(argnames(q)),symfun(findSymType(P,'symfun'),symvar(P)),q); % subs the dummy function
operateon(P,q)
Exending to other operations as defined in Matlab
operateon(2*P,q)
operateon(P^3,q)
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Dyuman Joshi
le 22 Déc 2023
Also, @Fritz Sonnichsen, if this answer solved your problem, please consider accepting the answer. The general idea is to accept the answer that is most fitting to the question asked.
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