The crossprod function in base R implements the MATRIX cross product, more familiarly known as "matrix multiplication".
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"R. Michael Weylandt" <michael.weylandt@gmail.com> wrote:

Try

library(pracma)
? cross

Michael Weylandt

On Thu, Nov 3, 2011 at 1:17 AM, 阮铮 <rz1991@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?
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>
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and provide commented, minimal, self-contained, reproducible code.


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