Passing Symbolic Variables into a function as parameters

Question

Benjamin Colety 2020-5-6

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/523526-passing-symbolic-variables-into-a-function-as-parameters

评论： Ameer Hamza 2020-5-7

I am trying to write a function that takes 2 symbolic equations, as well as the symbolic variables to solve for, in as parameters. The function is then supposed to solve for the 2 symbolic variables and then eliminate any solutions that contain imaginary numbers as you can see below.

syms x y
f = (x*y) == 1;
g = (x)+y == 0;
solution = testfunct(f, g, {x}, {y})
function [sols1 sols2] = testfunct(eq1, eq2 , t, s)
    sols = solve(eq1, eq2, [t s]);
    sols1 = sols.t(imag(sols.t)==0); % "Reference to non-existent field 't'"
    sols2 = sols.s(imag(sols.s)==0);
end

I receive an error saying seen in the comment. Now if this code works if I replace that line with

sols1 = sols.x(imag(sols.x)==0); %and the same for sols2 replacing x with y

Running whos gives me that t is a cell containing 1x1 sym which is x so I tried

sols1 = sols.(t{1,1})

which returns an error saying that 'Argument to dynamic structure reference must evaluate to a valid field name.' Even though t{1,1} = x and class(t{1}) = 'sym'.

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Answer 1

Ameer Hamza 2020-5-6

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/523526-passing-symbolic-variables-into-a-function-as-parameters#answer_430792

在 MATLAB Online 中打开

If you are willing to use the same variable name inside the function, then you can try this

syms x y
f = (x*y) == 1;
g = (x)+y == 0;
solution = testfunct(f, g, x, y) % <==== no need to pass as cell
function [sols1 sols2] = testfunct(eq1, eq2 , x, y)
    sols = solve(eq1, eq2, [x y]);
    sols1 = sols.x(imag(sols.x)==0); % "Reference to non-existent field 't'"
    sols2 = sols.y(imag(sols.y)==0);
end

If you want to use t and s as input variables, then you can use the following syntax

syms x y
f = (x*y) == 1;
g = (x)+y == 0;
solution = testfunct(f, g, x, y) % <==== no need to pass as cell
function [sols1 sols2] = testfunct(eq1, eq2 , t, s)
    sols = solve(eq1, eq2, [t s]);
    t_char = char(t);
    s_char = char(s);
    sols1 = sols.(t_char)(imag(sols.(t_char))==0); % "Reference to non-existent field 't'"
    sols2 = sols.(s_char)(imag(sols.(s_char))==0);
end