how can i do a multiplication between a column and a row?

when i make a product between a column and a row it says that it is incosistent row / column dimensions

[Walter Roberson]

Are you using the * operator or the .* operator? What is size() of the left vector and size() of the right vector? Which MATLAB release are you using?

[Jesus Francisco Serna Monsivais]

matlab 2017 and im using * A=[2 3 4]; B=[-2,1,3];

[Voss]

Those are both row vectors. A comma and a space do the same thing in concatenation, e.g., when defining a vector/matrix.

To make a column vector you can use semicolons:

A = [2 3 4];
B = [-2; 1; 3];
A*B

ans = 11

B*A

ans = 3×3

-4 -6 -8 2 3 4 6 9 12

Answer 1

[KSSV]

A = [2 3 4] ; 
B = [-2 1 3] ;
C1 = A*B'  % If you are expecting a dot product betwee them 

C1 = 11

C2 = A.*B  % element by element multiplication

C2 = 1×3

-4 3 12

C3 = A'*B  % if you expecting a 3x3 matrix 

C3 = 3×3

-4 2 6 -6 3 9 -8 4 12

Answer 2

[Walter Roberson]

The * operator is for algebraic matrix multiplication, also known as inner product. When you take A*B then size(A,2) must be the same as size(B,1) and the result is size(A,1) by size(B,2) . For example,

 A=[2;3;4], B=[-2,1,3]

A = 3×1

2 3 4

B = 1×3

-2 1 3

 
 size(A,2) == size(B,1)

ans = logical
   1

C = A*B

C = 3×3

-4 2 6 -6 3 9 -8 4 12

 [size(A,1), size(B,2)] == size(C)

ans = 1×2 logical array
   1   1

So if you want to use the * operator between two row vectors of the same length, then you need to transpose one of the two. If you transpose the first of them then the result would be a square matrix; if you transpose the second of them then the result would be a scalar.

If you want to multiply A(1) by B(1) and A(2) by B(2) and so on, then that is not the * operator, it is the .* operator

 A=[2,3,4], B=[-2,1,3]

A = 1×3

2 3 4

B = 1×3

-2 1 3

 C = A .* B

C = 1×3

-4 3 12