plot 1st order bessel derivative

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).

Answer 1

[Matt Kindig]

I think you need to use element-wise division with the z:

a=besselj(0, z) - besselj(1, z)./z;

[Md Rezaul Karim]

yes. cheack elementwise div or mul

Answer 2

[Walter Roberson]

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

[zamri]

thanks Walter, u're brilliant.