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How to get every term of a sum thats not multiplied by a convergent exponential function?

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Hansi K
Hansi K 2023-12-5
评论： Walter Roberson 2023-12-6
Ran in:
Hey, I need every term of a sum thats not multiplied by a convergent exponential function. In my case:
syms t
G = exp(-t)*cos(t) + 3*exp(-2*t)*sin(2*t) + 1/2*cos(4*t) + 1/5
G = 
What I need is stored in a variable. Is there any MATLAB function that fits my purpose?

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Walter Roberson
Walter Roberson 2023-12-5
Ran in:
Not exactly what you asked, but
syms t
G = exp(-t)*cos(t) + 3*exp(-2*t)*sin(2*t) + 1/2*cos(4*t) + 1/5
G = 
mapSymType(G, 'exp', @(varargin) 0)
ans = 
The reason it is not exactly what you asked is that you specified "not multipled by a convergent exponential function", implying that you would want a term with exp(5*t) [for example] to be retained as that is not convergent. So the parameter to the exp() needs to be examined to determine whether the exp() would be convergent or not.
  1 个评论
Walter Roberson
Walter Roberson 2023-12-6
Ran in:
syms t
G = exp(-t)*cos(t) + 3*exp(-2*t)*sin(2*t) + 1/2*cos(4*t) + 1/5 + 5*exp(7*t)
G = 
H = mapSymType(G, 'exp', @(EXPR) piecewise(LimitIsInf(children(EXPR,1)), EXPR, sym(0)))
H = 
function tf = LimitIsInf(EXPR)
var = symvar(EXPR,1);
if ~isempty(var)
tf = isAlways(limit(EXPR,var,inf)==inf, 'unknown', "true");
else
tf = isAlways(~isfinite(EXPR), 'unknown', "true");
end
tf = tf == symtrue;
end

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