# question about a simple matrix multiplication

Hi,
i have a matrix made of 4 lines and 3 columns, if i multiply it by a vector of 3 members(x, y, and z), will i get the same result than if i add a fourth column to the matrix (to have a 4x4 matrix)and the w component to the vector and if i multiply the new 4x4 matrix by the new vector (which have now four members) ?

PS :the column added to the matrix would be :
0
0
0
1

Originally posted by airseb:
[b]Hi,
i have a matrix made of 4 lines and 3 columns, if i multiply it by a vector of 3 members(x, y, and z), will i get the same result than if i add a fourth column to the matrix (to have a 4x4 matrix)and the w component to the vector and if i multiply the new 4x4 matrix by the new vector (which have now four members) ?

PS :the column added to the matrix would be :
0
0
0
1[/b]
Hello there the result for the first three elements is the same while the last member is 0 in case 1 and 1 in cse when you add the column to the matrix. Here I shw you with an example

``````
Case 1
Matrix M
1 0 0
0 1 0
0 0 1
0 0 0
Vector= [10,10,10] for our case its a column vector as shown below
1 0 0       10       10
0 1 0   X  10   = 10
0 0 1       10       10
0 0 0                    0

Case 2
Matrix M
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1
Vector= [10,10,10, 1] for our case its a column vector as shown below
1 0 0 0      10        10
0 1 0 0  X  10   =  10
0 0 1 0       10       10
0 0 0 1         1         1

``````

Hope this helps thanx
MMMovania

ok, if i have understood if the vector is a normal it change nothing in opengl ?