I understand that you require to export your function expression comining x,y variables in the expression form as indicated in the question. In MATLAB, you can make use of 'syms' command to define Symbolic Scalar Variables and Functions. Here is an example:
syms x y
cd = -((x^2 + y^2)^(1/2)*(-(79819630675297226055697*x^2*y^2)/364791569817010176000 + (29968083657371368688627119*x^2*y^4)/))... % your expression
cd_str = char(cd);
% Exporting this expression in a text file
fileID = fopen('cd_expression.txt', 'w');
fprintf(fileID, '%s\n', cd_str);
fclose(fileID);
% This expression can be then converted from 'char' to function expression
% by using 'str2sym' function
exp = str2sym(cd_str);
Refer to the following MathWorks documentations to know more:
Hope this helps. Thanks!
