something problem with diff
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Hello!This is my code.
syms x;
m = 5; h = 2*pi*x; q= besseli(5,h); k1 = h.^2-q; k = [m*q.*(h-3).*5 0 ; 0 q.*h-2 ]
a = det(k) pretty(diff(k(x)),x) Then,I got this message:
Invalid indexing or function definition. When defining a function, ensure that the body of the function is a SYM object. When indexing, the input must be numeric, logical or ':'.
What does it mean?
Thanks!
采纳的回答
Star Strider
2014-5-4
编辑：Star Strider
2014-5-4
You haven’t declared k as a function of x previously, so the Symbolic Math Toolbox assumes x is a subscript (that actually makes sense considering that k is a matrix).
Do this instead:
syms x;
m = 5;
h = 2*pi*x;
q= besseli(5,h);
k1 = h.^2-q;
k = [m*q.*(h-3).*5 0 ; 0 q.*h-2 ]
a = det(k)
fprintf('\n\ndiff(k,x) = \n\n') % This makes the output easier to read
pretty(diff(k,x)) % <== Changed line
produces:
diff(k,x) =
/ pi besseli(5, 2 pi x) 50 + #1 (2 pi x - 3) 25, 0 \
| |
\ 0, pi besseli(5, 2 pi x) 2 + pi x #1 2 /
where
besseli(5, 2 pi x) 5
#1 == pi besseli(4, 2 pi x) 2 - --------------------
x
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