Cross product of two vectors(function)

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Kyle
Kyle 2011-4-9
I need to create a function that calculates the cross product of two vectors V1 and V2.
V1 X V2=(Vy1*Vz2 - Vy2*Vz1)i + (Vz1*Vx2 - Vz2*Vx1)j + (Vx1*Vy2 - Vx2*Vy1)k
V1= Vx1i + Vy1j + Vz1k [-2,4,.5]
V2= Vx2i + Vy2j + Vz2k [.5,3,2]
Im completely lost at why i cant get this to work. The function should be something like crossprod[i j k] but i dont know how to implement i j k as inputs, for both vectors. Heres what i tried to do, not using i j k as inputs.
function [result]=cross_product(V1,V2)
%CROSS_PRODUCT calculates the cross product of two vectors.
V1=[v1x,v1y,v1z];
V2=[v2x,v2y,v2z];
i=(v1y*v2z - v2y*v1z);
j=(v1z*v2x - v2z*v1x);
k=(v1x*v2y - v2x*v1y);
result=i+j+k;
end

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采纳的回答

Paulo Silva
Paulo Silva 2011-4-9
V1=[v1x,v1y,v1z];
V2=[v2x,v2y,v2z];
Wrong code! you already have V1 and V2 not the other variables.
v1x=V1(1);v1y=V1(2);v1z=V1(3)
v2x=V2(1);v2y=V2(2);v2z=V2(3)
or just forget about those new variables and use only the V1 and V2
function [result]=cross_product(V1,V2)
%CROSS_PRODUCT calculates the cross product of two vectors.
i=(V1(2)*V2(3) - V2(2)*V1(3));
j=(V1(3)*V2(1) - V2(3)*V1(1));
k=(V1(1)*V2(2) - V2(1)*V1(2));
%result=i+j+k; %this is wrong
result=[i,j,k]; %this is right
end
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Kyle
Kyle 2011-4-9
The answer should be 6.5000 + 4.2500 + -8.0000 , how would would you implement that without adding them? Also i want to make a error check to make sure each vector has 3 components. is it possible to use nargchk for that inside the function?
Paulo Silva
Paulo Silva 2011-4-10
I was mislead by Kyle, James thanks for pointing the obvious error

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更多回答（1 个）

James Tursa
James Tursa 2011-4-10
OK. I will make a stronger statement this time. i+j+k is the wrong answer. You need to return a 3-vector, and i+j+k is not a 3-vector. Check the above code result against the built-in cross function and you will see what I mean. The above code result is wrong. Then reconsider my advice to return result=[i,j,k].

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