Create a local system of equations function from a set of anonymous functions

Question

Fernando 2023-7-7

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1993058-create-a-local-system-of-equations-function-from-a-set-of-anonymous-functions

编辑： Dyuman Joshi 2023-7-7

Hello,

I have a set of N anounimous functions which are created using this code

equations = {'@(x1,x2)x1.^2+x2-6','@(x1,x2)-2.5.*x1+x2.^2-2'};%Set your equations 
N = numel(equations);
f = cell(1,N);
for i = 1:N
    f{i} = str2func(equations{i});
end

The thing is, in a later part of the program I would like to use fsolve to solve the system of equation and fsolve requires the a function in this equivalent form:

function F = root2d(x)
F(1) = x(1).^2+x(2)-6;
F(2) = -2.5.*x(1)+x(2).^2-2;
end

where root2d is the function inputted in fsolve. I was wondering if there was a way to create a function in this form from the upper form or a way to use fsolve using the upper form?

Kind regards

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Answer 1

Paul 2023-7-7

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https://ww2.mathworks.cn/matlabcentral/answers/1993058-create-a-local-system-of-equations-function-from-a-set-of-anonymous-functions#answer_1269058

编辑：Paul 2023-7-7

在 MATLAB Online 中打开

One approach:

equations = {'@(x1,x2)x1.^2+x2-6','@(x1,x2)-2.5.*x1+x2.^2-2'};%Set your equations 
N = numel(equations);
f = cell(1,N);
for i = 1:N
    f{i} = str2func(equations{i});
end
F = @(x) cellfun(@(func) func(x(1),x(2)),f)
F = function_handle with value:
    @(x)cellfun(@(func)func(x(1),x(2)),f)
sol1 = fsolve(F,[2 2])
Equation solved.

fsolve completed because the vector of function values is near zero
as measured by the value of the function tolerance, and
the problem appears regular as measured by the gradient.
sol1 = 1×2
    1.8509    2.5743
F(sol1)
ans = 1×2
1.0e-13 *

   -0.0178    0.3109
[f{1}(sol1(1),sol1(2)) , f{2}(sol1(1),sol1(2))]
ans = 1×2
1.0e-13 *

   -0.0178    0.3109

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Answer 2

Dyuman Joshi 2023-7-7

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1993058-create-a-local-system-of-equations-function-from-a-set-of-anonymous-functions#answer_1269158

编辑：Dyuman Joshi 2023-7-7

在 MATLAB Online 中打开

Another approach (Note - requires Symbolic Toolbox)

equations = {'@(x1,x2) x1.^2+x2-6','@(x1,x2) -2.5.*x1+x2.^2-2'};%Set your equations 
f = str2sym(equations);
z = matlabFunction(f,"File", "root2d", "Vars",{symvar(f)});
out = fsolve(z,[2 2])
Equation solved.

fsolve completed because the vector of function values is near zero
as measured by the value of the function tolerance, and
the problem appears regular as measured by the gradient.
out = 1×2
    1.8509    2.5743
z(out)
ans = 1×2
1.0e-13 *

   -0.0178    0.3109