logspace equivalent and sin(x) [solved]

Hello, I have to solve a couple of exercises; the first one asks me to write with ":" the equivalents of this:

x=linspace(0, 10, 5);

x=linspace(-5, 5);

x=logspace(1, 3, 3);

x=logspace(1, 3, 5);

I solved the first by myself ( x=[0:2.5:10] ) because it's easy, but I really can't understand the others; actually I don't just want to solve the exercises but I want to understand if there is actually a method and how it is done.

Second one is this: A = {sin(x), x=1,2, ,1000}, I have to find how many elements of A are bigger than 1/2 using function SUM; actually I don't know that writing, I just started using Matlab, but even Matlab gives me an error, so maybe I thought it was wrong written; any guesses?

Answer 1

[Stephan]

x  = 10.^(1:3)  % x=logspace(1, 3, 3)

result = sum(A>0.5) % Number of elements in A bigger than 0.5

[Stephan]

x  = 10.^(1:0.5:3)  % x=logspace(1, 3, 5)

[Giacomo Lorenzi]

Thanks a lot!

Answer 2

[JESUS DAVID ARIZA ROYETH]

a=1;
b=3;
c=3;
logspace(a, b, c)==10.^(1:(b-a)/(c-1):b) %are equivalent 

on the other hand

x=1:1000;
A=sin(x);
total=sum(A>1/2)

Answer 3

[Giacomo Lorenzi]

Thanks guys, you were really helpful. However I still don't know how to solve the last

x = logspace(1, 3, 5)

it seems very tricky to me; the formula used for the previous one was pretty "standard", this is more "strange". Don't you know how to solve this too?

[Steven Lord]

You could "cheat" a little and look at what logspace does.

type logspace.m

I'm using type rather than edit to avoid accidentally modifying logspace. It's short enough that this won't display too much in the Command Window.