plot 1st order bessel derivative

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zamri
zamri 2012-7-31
评论： Md Rezaul Karim 2020-4-19
Hi all,
Can i ask if somebody can help me on why i got 'matrix dimension don't agree' thereby cannot get a plot for first order bessel derivative.
If i type 'diff(besselj(1,z),z)', i'd get 'besselj(0, z) - besselj(1, z)/z'
but then when i want to plot 'besselj(0, z) - besselj(1, z)/z' by typing:
format long
z = (0:1:100)';
a=besselj(0, z) - besselj(1, z)/z;
plot(z,a)
it'd give error as below:
??? Error using ==> minus
Matrix dimensions must agree.
Error in ==> Untitled at 4
a=besselj(0, z) - besselj(1, z)/z;
for some reason the second term gives 101x101 dimension which doesnt agree with the first term (101x1).

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采纳的回答

Matt Kindig
Matt Kindig 2012-7-31
I think you need to use element-wise division with the z:
a=besselj(0, z) - besselj(1, z)./z;

更多回答（1 个）

Walter Roberson
Walter Roberson 2012-7-31
besselj(1, z)/z is using the mrdivide operator ("/"), and so is the least-squares solution to X*z = besselj(1, z) . This will not be a vector.
If you want to construct the list of [besselj(1,K) / K] for K in 0 : 100, then you should use the rdivide arithmetic divide operator rather than the matrix divide operator:
besselj(1, z) ./ z

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