finding a number that satisfies given conditions

5 views (last 30 days)
Beaya on 25 Oct 2013
Answered: Walter Roberson on 4 Nov 2013
I need to find a floating point number x from the interval 1 < x < 2 such that: x ∗ (1/x) isn't equal to 1. I'ma beginner at Matlab and don't know how this can be done. I was given a clue that using integrals could help in solving this. Could anyone help me?
Beaya on 1 Nov 2013
I wrote a program to do this in C, but I must have done something wrong because the result was: 4.94066e - 324, which is smaller than 1.

Sign in to comment.

Answers (2)

Mike Hosea
Mike Hosea on 4 Nov 2013
Integrals? Not sure about that. A random search will finish faster. There are LOTS. You can use LINSPACE to generate evenly spaced trial numbers, or you can us 1 + rand(1,n) to generate n random numbers between 1 and 2. Then you can check the condition using MATLAB's elementwise array operators: bool = x.*(1./x) ~= 1. Notice the .* instead of *, since * without the . is matrix multiplication. Same thing for division. Actually if you generate a boolean array that way from a set of trial numbers, you can also extract the results from your trial vector x using MATLAB's logical indexing, e.g. x(bool). Try it!

Walter Roberson
Walter Roberson on 4 Nov 2013
Do a binary search over the interval realmin() to 1, to find the boundary point.


Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!