Creating symbolic function with array for argument

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Benoit Cabot 2024-3-8

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2092066-creating-symbolic-function-with-array-for-argument

评论： Benoit Cabot 2024-3-8

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

Hi,

I am trying to understand how to use mutli dimension array with symbolic function. I am not sure why I get an error for the symolic function when the input argument is two dimension.

x = sym ('x', [2 1]);
y = sym( 'y', [1 2]);
z = sym( 'z', [2 5]);  
f(x,y,z)=(x(1,1)+y(1,1)+z(1,1));
Error using sym/cat>checkDimensions
CAT arguments dimensions not consistent.

Error in sym/cat>catMany (line 33)
[resz, ranges] = checkDimensions(sz,dim);

Error in sym/cat (line 25)
    ySym = catMany(dim, args);

Error in sym/horzcat (line 19)
    ySym = cat(2,args{:});

Error in indexing (line 1033)
            C = symfun(sym(R),[inds{:}]);

if I change the variable to

x = sym ('x', [1 1]);
y = sym( 'y', [1 2]);
z = sym( 'z', [1 5]);  
f(x,y,z)=(x(1,1)+y(1,1)+z(1,1));

it works fine, I am not sure I understand why

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VBBV 2024-3-8

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symfun operates using scalars more efficiently. The function f has three independent variables, x y and z . So, the function needs inputs to three variables

x = sym ('x');

y = sym( 'y');

z = sym( 'z');

f(x,y,z)=symfun(x+y+z,[x,y,z])

f(x, y, z) =

X=[1 ; 1];

Y=[1 1];

Z=[1 2 3 4 5; 6 7 8 9 0];

f(X(1,1),Y(1,1),Z(1,1)) + f(X(2,1),Y(1,1),Z(1,1)) + f(X(1,1),Y(1,1),Z(1,1)) + f(X(1,1),Y(1,2),Z(1,1)) + ...

f(X(1,1),Y(1,1),Z(1,1)) + f(X(1,1),Y(1,1),Z(2,5))

ans =

Benoit Cabot 2024-3-8

thank you

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采纳的回答

Walter Roberson 2024-3-8

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2092066-creating-symbolic-function-with-array-for-argument#answer_1422906

在 MATLAB Online 中打开

You cannot create symfun that expect non-scalars as parameters.

symfun takes all of the provided parameters, horzcat()'s them together, and creates individual parameters for the results.

x = sym ('x', [1 2]);

y = sym ('y', [1 2]);

f(x, y) = x(1) + x(2) + y(1) + y(2)

f(x1, x2, y1, y2) =

Notice that it has become a function of four parameters.

x = sym ('x', [2 1]);
y = sym ('y', [2 1]);
f(x, y) = x(1) + x(2) + y(1) + y(2)
Error using symfun.validateArgNames
Second argument must be a scalar or vector of unique symbolic variables.

Error in symfun (line 102)
            y.vars = symfun.validateArgNames(inputs);

Error in indexing (line 1033)
            C = symfun(sym(R),[inds{:}]);