## Error using * Inner matrix dimensions must agree urgent help please.

Asked by Or Peer

### Or Peer (view profile)

on 28 Apr 2019
Latest activity Commented on by Stephen Cobeldick

### Stephen Cobeldick (view profile)

on 29 Apr 2019
Accepted Answer by Geoff Hayes

### Geoff Hayes (view profile)

I got this prompt and I dont know how to solve it.
function water_vec=water_light_ray_vec(air_vec,refractive_index)
normal_vec=[0
0
1];
% normal_vec=[0;0;1];
water_vec=(air_vec-normal_vec*(air_vec*normal_vec-sqrt(air_vec*normal_vec-1+refractive_index^2)))/refractive_index ;
end
refractive index size is 1.33 1 by 1
normal_vec is [0
0
1]
air_vec is [-0.173230940506992
-0.116707951859014
0.667867059147687]
help will be very appreciated.

#### 1 Comment

Stephen Cobeldick

### Stephen Cobeldick (view profile)

on 29 Apr 2019
@Or Peer: you need to learn the differernce between array and matrix operations:

### Geoff Hayes (view profile)

Answer by Geoff Hayes

### Geoff Hayes (view profile)

on 28 Apr 2019

Or - the error is due to the following multiplciation
air_vec*normal_vec
where both arrays/vectors are 3x1 and so the error message makes sense. What do you want to be doing here? Multiplying the two to get a scalar or do you want to keep the 3x1 dimensions?

Or Peer

### Or Peer (view profile)

on 28 Apr 2019
I would like to keep the 3x1 dimensions, thank you for the help.
Geoff Hayes

### Geoff Hayes (view profile)

on 29 Apr 2019
try
air_vec .* normal_vec