Creating an array of dependent symbolic variable

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Abinav 2020-10-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/612911-creating-an-array-of-dependent-symbolic-variable

评论： Abinav 2020-10-14

采纳的回答： madhan ravi

在 MATLAB Online 中打开

Hi,

I need to create 'N' equations based on user input 'N' which is a natural number.

Each equation is supposed to have a variable A which is a dependent on x. This 'A' term is different for each equation. Equation1 will have A1, equation2 will have A2 and so on.

I am creating this term using the expresion below.

A = sym('A', [1 N]);

This gives me symbolic variables A1, A2, A3... AN. But the problem is these terms are just symbolic variables and not dependent on x. So if I differentiate the equation with respect to x, these terms dissappear. If I use A(x) to create the variable (like a normal dependent variable), it returns a 1x1 symbolic function instead of 1xN symbolic variables.

A(x) = sym('A', [1 N]);

The above equation creates 1xN symbolic variables but the output is of type 1x1 symbolic function. Is there a way to isolate each term from this function or is there any other way to create a dependent variable array.

Thanks

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madhan ravi 2020-10-13

What’s your application by your idea?

Abinav 2020-10-13

I have 'N' sections and each section has an equation.

The equations have some common terms and different terms which depend on the boundary conditions. I am creating those equations through a loop and conditional statements which will be solved later. So, I need the variable 'A' to be an array so that I can add it to the equations while iterating through the loop.

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Answer 1

madhan ravi 2020-10-13

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https://ww2.mathworks.cn/matlabcentral/answers/612911-creating-an-array-of-dependent-symbolic-variable#answer_513046

编辑：madhan ravi 2020-10-13

在 MATLAB Online 中打开

A(x) = str2sym(regexprep(char(A), '(\_?\d)+', '$0(x)'))

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madhan ravi 2020-10-13

编辑：madhan ravi 2020-10-13

在 MATLAB Online 中打开

 A(x) = str2sym("A" +(1:N)+"(x)")
 Wanted = formula(A)
 Wanted(2)

[Too many edits in mobile is so painful ;)]

Abinav 2020-10-14

Thanks. It worked.

Sorry to put you through that.

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Answer 2

Steven Lord 2020-10-13

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https://ww2.mathworks.cn/matlabcentral/answers/612911-creating-an-array-of-dependent-symbolic-variable#answer_513036

在 MATLAB Online 中打开

syms A [1 2]
eq1 = A(1)+2*A(2) == 42
eq2 = 3*A(1)-4*A(2) == 99
S = solve(eq1, eq2)
A1 = S.A1
A2 = S.A2
subs(eq1)

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Abinav 2020-10-13

I think you didn't get my question.

I need to create an array of dependent symbolic varaible, not just symbolic variables. Something like

A = [A1(x) A2(x) A3(x)]

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