How do I create a MATLAB function from some symbolic variables and a structure of symbolic variables?

Hi everyone, and thanks in advance for the replies.

My code start like this:

x = {'X','Y','vx','vy'};
syms(x)
x=cell2sym(x);
assume(x,'real')

mystruct.a = sym('a',[1,2],'real');
mystruct.b = sym('b',[1,2],'real');

M = [x(1),x(2);mystruct.a(1),mystruct.b(1)];

What I want is to generate in the current folder a .m function file like this:

function M = myfunction(x,mystruct)

X = x(1);
Y = x(2);
a1 = mystruct.a(1);
b1 = mystruct.b(1);

M = [X,Y;a1,b1];

end

namely, in which its inputs are exactly (x,mystruct) and not (X,Y,a1,b1).

I tried to use the "matlabFunction" command in this way:

matlabFunction(M,'file','myfunction','Vars',{x,mystruct},'output',{'M'});

but it doesn't work because 'Vars' does not accept a struct (like mystruct). Does anyone knows how to overcome this problem or can propose me other approaches?

Answer 1

[Ananya Tewari]

I understand that you want your inputs to be (x,mystruct) for 'Vars' field matlabFunction().

The 'vars' field of matlabFunction() only accepts character vector, 1-d cell array of character vector or array of symbolic variables. Structres are not accepted by the 'Vars' field.

Here is a workaround for the above given code:

Rather than using structure we can use array of symbolic variables

x = {'X','Y','vx','vy'};
syms(x)
x=cell2sym(x);
assume(x,'real')

% creating two sym variables rather than structure
a = sym('a',[1,2],'real');
b = sym('b',[1,2],'real');
% creating array for the sym variables
y = [a(1) b(1)];

M = [x(1),x(2);y(1),y(2)];

matlabFunction(M,'file','myfunction','Vars',{x, y},'output',{'M'});

[Manuel Coccia]

Thank for your reply.

Yes, I want to create a function with input x and mystruct.

Unfortunately, I cannot replace the structure mystruct with an array of symbolic variables, because this structure is utilized in many other parts of my code. Also a compromise solution like this:

y = [mystruct.a(1),mystruct.b(1)]       % (*)

M = [x(1),x(2);y(1),y(2)];

matlabFunction(M,'file','myfunction','Vars',{x, y},'output',{'M'});

cannot be performed because mystruct is too big in my real code to do the step (*) manually.

So, since the matlabFunction() command has this limitation, do you know other approaches to solve the problem?

Thanks again.