eval() is too slow to numerically evaluate a function with X(t) and Y(t).

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Perico Nasdemico
Perico Nasdemico 2023-4-20
评论： Perico Nasdemico 2023-4-22
Hello,
I have a symbolic vector function, Vfun, that depends of two symbolic variables, X(t) and Y(t).
I want to evaluate Vfun for a series of numerical values for X and Y. Here's what I've tried. It works, but it's quite slow.
%% SETUP
syms X(t) Y(t) % (here the "(t)" isn't very relevant, but, I'll need to be able to use diff(Vfun,t) later on)
Vfun = [2*X + Y ; cos(X)*X^2 + Y^3 ; 3 + sin(Y)]; % (actually generated by an algorithm I can't change)
N = 40000;
Xnum = rand(1,N);
Ynum = rand(1,N);
%% TRYING TO EVALUATE Vfun WITH Xnum AND Ynum
tic
Mresults = zeros(3,N);
for j = 1:N
X = Xnum(j);
Y = Ynum(j);
Mresults(:,j) = subs(Vfun);
end
toc
I suspect the problem lies in the subs() function.
I've tried to use matlabFunction(), but it doesn't work and I don't know how to remove the "(t)"
Any ideas? I doesn't need to be ultra-fast, just something more reasonable.
Thank you in advance

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采纳的回答

James Tursa
James Tursa 2023-4-20
编辑：James Tursa 2023-4-20
Ran in:
Something like this?
syms X(t) Y(t)
Vfun = [2*X + Y ; cos(X)*X^2 + Y^3 ; 3 + sin(Y)]
Vfun(t) = 
syms x y
vfun = subs(Vfun,[X Y],[x y])
vfun(t) = 
f = str2func(['@(x,y)' vectorize(char(vfun))]) % explicit code with no t
f = function_handle with value:
@(x,y)[2.*x+y;x.^2.*cos(x)+y.^3;sin(y)+3]
g = matlabFunction(vfun(0)) % using matlabFunction( ) with arbitrary t=0
g = function_handle with value:
@(x,y)[x.*2.0+y;x.^2.*cos(x)+y.^3;sin(y)+3.0]
N = 40000;
Xnum = rand(1,N);
Ynum = rand(1,N);
fnum = f(Xnum,Ynum);
gnum = g(Xnum,Ynum);
isequal(fnum,gnum)
ans = logical
1

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