Differentiation with respect to variable which has been changed to numeric type

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Ali Baig
Ali Baig 2017-11-7
评论： Ali Baig 2017-11-8
Hello, consider the given expression. Here x and y are symbolic variables and X and Y are numeric matrices of same size. All other variables are scalars.
RVector = ( (x - X).^2 + (y - Y).^2 + (alpha_C * d_C).^2 ) .^q;
When I execute the the following lines
x = X;
y = Y;
R_0Vector = double((subs(RVector)));
x and y becomes numeric variables. (Right?) Now, after the execution of above lines, how can I differentiate RVector with respect to x and y?

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Walter Roberson
Walter Roberson 2017-11-7
The easiest way is to avoid the problems associated with assigning a new value to a symbolic variable that has been used in other expressions. Do not do the assignments x = X and y = Y. Instead do
R_0Vector = double(subs(Rvector, {x, y}, {X, Y}));
and then x and y will still be symbolic, allowing you to continue on with
diff(Rvector, x)

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