# Multiplication of matrix

1. Jan 10, 2010

### Cosmossos

Hello,
I came to some problems with multiplcation of some matrices.
how do I multply this:
x
y
z

with
a
b
c

those are vertical vectors.
thanks

Last edited: Jan 10, 2010
2. Jan 10, 2010

### rochfor1

It's not possible to multiply those two vectors using matrix multiplication. To multiply two matrices, the number of columns of the first must equal the number of rows of the second. Both of your matrices are 3x1 and cannot therefore mutliply each other. If you were to transpose one, then you could multiply them.

3. Jan 10, 2010

### Landau

...and that would be their inner product.

4. Jan 10, 2010

### Cosmossos

I know , that's why I didn't have a clue what to do. the problem is that I don't have a choice becasue I got integral like this:

And it's given in the question

5. Jan 10, 2010

### rochfor1

Only when you transpose the first vector. If you transpose the second vector you will get a 3x3 matrix.

6. Jan 10, 2010

### Landau

@rochfor: true
@Cosmossos: you are forgetting the psi which is in between!

7. Jan 10, 2010

### Cosmossos

so? I can put the psi in the beginning ,no?

I got the same problem here:
How do I make it look like: ???
It makes sense if I think about it as a scalar product, but I don't know how ...

Last edited: Jan 10, 2010
8. Jan 10, 2010

### Landau

Of course not, since then you end up with your first question about an undefined product! You can't evaluate an integral if you don't understand what the terms in the integrand mean.

9. Jan 10, 2010

### Cosmossos

so what do I do? Psi is a fucntion after all Can you reread my question? I added some things

10. Jan 10, 2010

### Cosmossos

Thanks I got it!!!

11. Jan 10, 2010

### elibj123

I believe you are trying to take the deger of the column vector, don't forget that deger acts also as a transpose operator (and also complex conjugation), so $$\psi ^{+}$$ is a row vector with components $$(\psi_{1}*, \psi_{2}*)$$

P.S. Are you taking a course in the Technion?