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vectorized operations on symbolic functions
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Muhammad Uzair
am 19 Feb. 2024
Bearbeitet: Torsten
am 21 Apr. 2024
Hi, Can we apply vectorized operations on symbolic functions to avoid loops?
syms x1 x2 x3; % symbolic variables
y = x1^3/3 + x2^2/2 - x3; % symbolic function y
X = rand(500,3) % each row representing a combination of x1 x2 x3
I used for loop, but it is taking more time.
y_values = zeros(size(X,1))
for ii = 1:size(X,1)
y_values(ii) = subs(y, [x1, x2, x3], X(ii,:));
end
I have tried following but since there is inconsistency between sizes of old and new it don't work for me.
y_values = subs(y, [x1, x2, x3], X); % Evaluate the function for all combinations in matrix X
Thanks
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Akzeptierte Antwort
Hassaan
am 19 Feb. 2024
Bearbeitet: Hassaan
am 19 Feb. 2024
syms x1 x2 x3; % symbolic variables
y = x1^3/3 + x2^2/2 - x3; % symbolic function y
% Generate a random matrix X with 500 rows and 3 columns
X = rand(500, 3); % each row representing a combination of x1 x2 x3
% Evaluate the symbolic function y for each row in X
% Convert the matrix X to a cell array where each row is a separate cell
X_cell = num2cell(X, 2);
% Use cellfun to apply the subs function to each cell (row) of X_cell
y_values = cellfun(@(row) subs(y, [x1, x2, x3], row), X_cell);
% Convert y_values to a double array if needed
y_values = double(y_values);
disp(y_values(1:10))
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2 Kommentare
Weitere Antworten (5)
Matt J
am 19 Feb. 2024
Bearbeitet: Matt J
am 19 Feb. 2024
syms x1 x2 x3; % symbolic variables
y = x1^3/3 + x2^2/2 - x3; % symbolic function y
X = rand(500,3); % each row representing a combination of x1 x2 x3
ynum=matlabFunction(y) %convert to a numeric function
yvalues=ynum(X(:,1),X(:,2),X(:,3))
0 Kommentare
Dyuman Joshi
am 19 Feb. 2024
Better to use a function handle -
x = rand(500,3);
y = @(x) x(:,1).^3/3 + x(:,2).^2/2 - x(:,3);
out1 = y(x)
For more information, refer to these documentation pages -
2 Kommentare
Christine Tobler
am 19 Feb. 2024
Your best approach then might be to make your input variables have the individual pages already as a third dimension:
x = randn(3, 1, 500);
y = randn(1, 6, 500);
z = x.*y;
size(z)
The formula here is of course completely made up, it would depend on what your formula for this 3x6 matrix is.
Aquatris
am 19 Feb. 2024
Bearbeitet: Aquatris
am 19 Feb. 2024
Yet another method, you can define your symbolic parameter as a matrix symbolic
n = 500;
X = sym('X', [500 3]);
% I assume here you want a element wise power ('.^') instead of matrix power
y = X(:,1).^3/3 + X(:,2).^2/2 - X(:,3); % symbolic function y
X_val = rand(500,3); % each row representing a combination of x1 x2 x3
y_values = double(subs(y, X, X_val)) % Evaluate the function for all combinations in matrix X
size(y_values)
0 Kommentare
Walter Roberson
am 19 Feb. 2024
syms x1 x2 x3; % symbolic variables
y = x1^3/3 + x2^2/2 - x3; % symbolic function y
X = rand(500,3); % each row representing a combination of x1 x2 x3
y_values = double(subs(y, {x1, x2, x3}, {X(:,1), X(:,2), X(:,3)}));
y_values(1:5)
0 Kommentare
Torsten
am 21 Apr. 2024
Bearbeitet: Torsten
am 21 Apr. 2024
rng("default")
syms x1 x2 x3; % symbolic variables
y = x1^3/3 + x2^2/2 - x3; % symbolic function y
X = rand(500,3) % each row representing a combination of x1 x2 x3
y_values = arrayfun(@(i)double(subs(y,[x1,x2,x3],[X(i,1),X(i,2),X(i,3)])),1:size(X,1))
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