# How do i write a code which can calculate the cross production of two vectors?

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yang-En Hsiao on 24 Sep 2019
Edited: Bruno Luong on 24 Sep 2019
How do i write a code which can calculate the cross production of two vector ? Both of these two vectors are 1 by 5 vector
At first, i write the code like
a=randn(1,5);
b=randn(1,5);
cross_c=cross(a,b)
or
a=randn(1,5);
b=randn(1,5);
cross_c=cross(a,b,5)
But the window always show me
A and B must be of length 3 in the
dimension in which the cross
product is taken.
How do i write a code which can calculate the cross production of these two 1 by 5 vectors?

James Tursa on 24 Sep 2019
Cross products are defined for 3-element vectors only. Maybe you could tell us what your definition of this for 5-element vectors would be. What are you using this for?
yang-En Hsiao on 24 Sep 2019
In fact,the 1 by 5 vectors are the null space for two the MIMO channel,5 by 3 matrix H_A and H_B,and assume they have two null space basis
[uA,sA,vA]=svd(H_A),so uA is a 5 by 5 matrix,and "a" is the sum of two null space vector,which is 1 by 5 vector.
[uB,sB,vB]=svd(H_B),so uB is a 5 by 5 matrix,and "b" is the sum of two null space vector,which is 1 by 5 vector.
Now i want to find an vector which is orthogonal to "a" and "b" ,that is why i want to calculate the cross product between "a" and "b"

Bruno Luong on 24 Sep 2019
Edited: Bruno Luong on 24 Sep 2019
If A and B are 5 x 1
null([a;b])
returns a (5 x 3), 3 vectors in R^5 basis of NULL(SPAN(a,b))