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Two basic MATLAB problems help

Asked by Paul
on 26 Sep 2013
Latest activity Answered by Jan Simon
on 27 Sep 2013

Hi, I'm a student studying engineering and I have my first exam tomorrow on MatLab. I'm going through some practice problems and ran into two that I don't understand, I posted them below and was wondering if anyone could help me out! Thanks

6) Assume that the function *diff* does not exist.  Write your own expression(s) to accomplish the same thing for a vector.
7)  Find expressions that will evaluate the function f of two variables x and y:
	f(x,y) = 3*x - y
where x ranges from 1 to 2 and y ranges from 1 to 5.  


Cedric Wannaz
on 27 Sep 2013

For 6, build an numerical example, e.g. with a vector

 x = [4, 1, 7, 9]

if you understand what DIFF does, it is easy to emulate it with a simple loop (hint: it doesn't start on the first element).

For 7, you can certainly build two nested loops over elements of x and y and build an array of solutions, but you could also consider an approach where X and Y are appropriate arrays of values of x and y, and perform the evaluation of f in one matrix equation. Look at the doc of MESHGRID to understand this comment.

Walter Roberson
on 27 Sep 2013

#6, diff() can be done without any loop.

#7 can be done without any loop and without any meshgrid (or ndgrid. or repmat)

Jan Simon
on 27 Sep 2013

These problems are not complicated. So I wish you good luck for your first exam tomorrow.


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2 Answers

Answer by Image Analyst
on 27 Sep 2013

Hint: type out vec(1:end-1) and vec(2:end) and see what that shows.


Answer by Jan Simon
on 27 Sep 2013

#7: When x ranges from 1 to 2 only, you can write down the equation for x=1 and x=2 manually. If you define y=1:5, the work is done already.


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