- placed the first term r.^2 in parenteses
- Added a dot in front of the first sin()
- added a dot in front of the last division operator
- added parentheses to the last term as below:

# I can not find an error in the expression

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Hi all,

I'm new to matlab, so sorry for the stupid question.

I tried to fix the errors, but could not find another. I give the code of the expression that I want to get in Python and ask to fix this expression for matlab. Also, if not difficult, please share some good materials for learning matlab.

Thanks!

In MatLab with error:

fun = @(r,t,p) r.^2*sin(p).*(exp(i*(r.*sin(t).*cos(p) + r.*sin(t).*sin(p) + r.*cos(t))))*4*pi/(r.^2 - 4)

q = integral3(fun,0,1.99,0,pi,0,pi*2)

Error using * Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of rows in the second matrix. To

perform elementwise multiplication, use '.*'.

##### 0 Comments

### Accepted Answer

Katie
on 24 Oct 2019

Hi! It looks like you're really close! You're just missing a couple dots in front of some of your multiplication and division operators. Below is the fixed expression. I also added in a couple sets of parentheses.

fun = @(r,t,p) (r.^2).*sin(p).*(exp(i*(r.*sin(t).*cos(p) + r.*sin(t).*sin(p) + r.*cos(t)))).*((4*pi)./(r.^2 - 4))

Summary of changes:

((4*pi)./(r.^2 -4))

##### 2 Comments

### More Answers (1)

Jim Riggs
on 24 Oct 2019

Edited: Jim Riggs
on 25 Oct 2019

It's hard to say without seeing how the variables r, t, and p are defined. If r and p are vectors of different length, then the expression:

r.^2*sin(p)

will cause a problem, because it implies a matrix multiplication of a vector of length r and one of length p. (here r.^2 is a vector with the same length as r, and sin(p) is a vector with the same length as p)

In Matlab, if you want to multiply vector r and vector p, they both must be the same length, and one must be a row vector, and the other a column vector. For example, if r and p are the same size but both are row vectors, then r*p will give an error (This works in python, but not in matlab, although in python, this will perform element-wise multiplication). To perform the matrix multiply in matlab you would have to transform one of them:

r*p'

If you want to perform element-wise multiplication, r and p must still be the same length, and you use .*

r.*p

or

r.^2.*sin(p)

##### 2 Comments

Katie
on 24 Oct 2019

For this particular case, you don't need to define r, t,and p. They are terms in the expression 'fun' that is being integrated over from 0<r<1.99, 0<t<pi, and 0<p<2pi. When you run the two lines of code you get the following:

fun = @(r,t,p) (r.^2).*sin(p).*(exp(i*(r.*sin(t).*cos(p) + r.*sin(t).*sin(p) + r.*cos(t)))).*((4*pi)./(r.^2 - 4))

q = integral3(fun,0,1.99,0,pi,0,pi*2)

%output:

q =

1.1211e-07 - 1.2308e+02i

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