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crossp3

Compute cross product of multiple vectors of length 3.

Available in version 5.1.0 and later.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"  ; This library is automatically loaded
                                                             ; from NCL V6.2.0 onward.
                                                             ; No need for user to explicitly load.

	function crossp3 (
		a [*][3] : numeric,  
		b [*][3] : numeric   
	)

	return_val  :  same type and shape of a

Arguments

a

A two dimensional array of any numeric type. The right dimension must be of length 3 [x,y,z directions].

b

A two dimensional array of any numeric type. The right dimension must be of length 3 [x,y,z directions].

Return value

The results are returned in an array of the same shape and type as a.

Description

The following is applied to each triplet.

     c(0) = a(1)*b(2)-a(2)*b(1)
     c(1) = a(2)*b(0)-a(0)*b(2)
     c(2) = a(0)*b(1)-a(1)*b(0)

Examples

The following require that contributed.ncl be loaded prior to invoking the function.

 load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"

Example 1

  a  = (/ (/ 2,  -3,  -1/) \
        , (/-4, 9.3, 0.4/) /)
  b  = (/ (/ 1,   4,  -2/) \
        , (/-9,   0,-5.4/) /)

  ab = crossp3(a,b) 
  ba = crossp3(b,a)

  print("ab="+ab +"   ba="+ba)
The output would be:
    (0,0)	ab=10       ba=-10
    (0,1)	ab=3        ba=-3
    (0,2)	ab=11       ba=-11

    (1,0)	ab=-50.22   ba=50.22
    (1,1)	ab=-25.2    ba=25.2
    (1,2)	ab=83.7     ba=-83.7