Cross product of two 2D vectors

Question

Can someone provide an example of a function that returns the cross product of TWO strong> 2d vectors? I am trying to implement this algorithm .

C code would be great. Thanks.

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EDIT: Found another way to do this, which works for 2D and doesn't work easily.

bool tri2d::inTriangle(vec2d pt) { float AB = (pt.y-p1.y)*(p2.x-p1.x) - (pt.x-p1.x)*(p2.y-p1.y); float CA = (pt.y-p3.y)*(p1.x-p3.x) - (pt.x-p3.x)*(p1.y-p3.y); float BC = (pt.y-p2.y)*(p3.x-p2.x) - (pt.x-p2.x)*(p3.y-p2.y); if (AB*BC>0.f && BC*CA>0.f) return true; return false; } 

Answer 1

(Note: The cross product of two vectors is defined only in 3D and 7D space .)

The code computes the z-component of 2 vectors lying on the xy plane:

 vec2D a, b; ... double z = ax * by - bx * ay; return z; 

Answer 2

Mathworld cross product