R help - Nov 2011 - Question about Calculation of Cross Product

The function of crossprod in R puzzled me.
I would like to calculate the cross product of two vectors. According to my text
book, it defines like this:
a = (ax, ay, az)
b = (bx, by, bz)
then, the cross product of a and b is:
a X b = (ay*bz-az*by, az*bx-ax*bz, ax*by-ay*bz)
It can also write in a determinant format.


But the crossprod or tcrossprod function in R appeared not calculate the cross
product. Suppose I enter this:
> a = c(1, 2, 3)
> b = c(2, 3, 4)
> ab = crossprod(a, b)
> ab
     [,1]
[1,]   20
> ab = tcrossprod(a, b)
> ab
     [,1] [,2] [,3]
[1,]    2    3    4
[2,]    4    6    8
[3,]    6    9   12


Does any know how to calculate cross product in R. Or I have to write the
function myself?
	[[alternative HTML version deleted]]

Try

library(pracma)
? cross

Michael Weylandt

On Thu, Nov 3, 2011 at 1:17 AM, ?? <rz1991 at foxmail.com>
wrote:
> The function of crossprod in R puzzled me.
> I would like to calculate the cross product of two vectors. According to my
text book, it defines like this:
> a = (ax, ay, az)
> b = (bx, by, bz)
> then, the cross product of a and b is:
> a X b = (ay*bz-az*by, az*bx-ax*bz, ax*by-ay*bz)
> It can also write in a determinant format.
>
>
> But the crossprod or tcrossprod function in R appeared not calculate the
cross product. Suppose I enter this:
>> a = c(1, 2, 3)
>> b = c(2, 3, 4)
>> ab = crossprod(a, b)
>> ab
> ? ? [,1]
> [1,] ? 20
>> ab = tcrossprod(a, b)
>> ab
> ? ? [,1] [,2] [,3]
> [1,] ? ?2 ? ?3 ? ?4
> [2,] ? ?4 ? ?6 ? ?8
> [3,] ? ?6 ? ?9 ? 12
>
>
> Does any know how to calculate cross product in R. Or I have to write the
function myself?
> ? ? ? ?[[alternative HTML version deleted]]
>
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