Finding the Unit Vector in the Direction of a Vector using Matrices and MATLAB

[andyintranzit]

Hey guys,

Sorry if this is the wrong forum. Someone bump it across if its not.

This is a question on one of my tests (im doing my first semester of Physics at university) and its got to do with the program Matlab.


We have two vectors u and v. Which of the following gives us the unit vector in the direction of v, starting from u?

a) (v-u)/(u*u')
b) (v-u) * (v - u)
c) (v-u)./mag(v-u)
d) (v-u) / (sqrt(v-u)*(v-u)')




'I understand some basic matrix algebra, but I am still pretty spun out about matrices. can someone guide me through this? (a) thanks!

 

[andyintranzit]

ok.. i think i can eliminate the middle two because...

for b) you can't multiply two identical vector matrices together? cause they'll be in the same form?

and for c) I am pretty sure that mag() isn't a Matlab function at all...

 

[uart]

The answer is d.

No mag() is not a MATLAB function, perhaps they meant abs() which is a function to return the magnetude of a complex value. In any case sqrt(v-u)*(v-u)') is the correct divisor to normalize it.

BTW you know that for row vectors x and y that x*y' gives the dot product of x and y, right? If you happen to be using column vectors then it's just the simple modification of using x'*y of course.