matlab code help..

Hi everyone

This is my first post and I am totally new to Matlab, started a couple of weeks back been practicing and all but already got an assignment to come up with a Matlab code. I have a pretty simple question

Say I have a set of data like x = [-2 3 -4 5 -2 5 -3 10 8 9 ]. The set represents basically +ve and -ve peaks. I am trying to get a loop to do the difference between each 2 points along the vector set(difference between -2&3 3&-4 -4&5 5&-2 and....so on).Could someone give me some ideas of how to get around this...would really appreciate the help

thank you

Answer 1

[Wayne King]

Welcome to MATLAB! One of the great things about MATLAB is that it handles matrices (and vectors) easily. I would recommend you try to avoid loops as much as you can. There is a MATLAB function diff() that does just want you need.

x = [-2 3 -4 5 -2 5 -3 10 8 9];
y = diff(x);

Of course, if your homework is specifically to write a loop to do this, then let me give you some hints (I don't want to just write the loop for you)

The basic assignment you need is something like:

y(n) = x(n+1)-x(n);

where y is the output and x the input. Now that takes the difference of elements in a particular order, the same order as diff(). If you want it the other way:

   y(n) = x(n)-x(n+1);

Since MATLAB indexes from 1, you have to think about the range of your n in the for loop. You want to start at 1, but think about how far the n go grow since you are trying to access x(n+1)

[abishai]

Hi Wayne

thanks for the reply.I am trying to implement it but in vain. I have my set of data, say

x = [...] with some -ve values

a = abs(x) %which turns the set into all +ve values

i=(1:34)

b =a(i)

b = a(i) - a(i+1)

not coming out right, could you please tell me the problem, it seems that I can do without the loop right?

thanks

[Image Analyst]

a(i+1) is longer. It goes from a(2) to a(35). Try this

b = [a(i) 0] - a(i+1)

or similar. Also it's not recommended to use i (the imaginary constant) as a variable.

[Jan]

Yes, it works without a loop. Did you try "diff(a)"?

What does "not coming out right" exactly mean? It is much better to explain the error or problem in the forum instead of only mention that there is one.

Answer 2

[abishai]

solved it Just had to take off the following b = a(i)

thanks a lot guys still got to finish the code..its going to take a while