MATLAB: Negative x axis meaning

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Hello

I have a vector plot created from multiple functions. The x axis values are incorrect and some are negative. Does matlab assign x axis in order to generate a suitable graph?

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This is confusing as a question. You have a plot of some numbers. Some of them are negative. Of course MATLAB will extend the axis out to include the values you plotted. That some of them are negative and you don't want them to be is irrelevant, since MATLAB just plots what you tell it to plot.

If you don't want anything negative, then force it to be so in advance. Or correct what ever bug was there to prevent that from happening.

I suppose, you can always set the axis limits after the fact, effectively ignoring any negative values. But that just closes your eyes to the problem. I would suggest fixing the problem, rather than just pretending it does not exist.

Related Solutions

MATLAB: How do you enter the command for a cube root

Two simple options:

x^(1/3)

Or,

nthroot(x,3)

Be very careful though. If x is negative, it will return a complex number, because there are indeed THREE cube roots of a negative number. Two of them are complex. nthroot will give you the root you would expect however.

(-2)^(1/3)
ans =
      0.62996 +     1.0911i
nthroot(-2,3)
ans =
      -1.2599

In your case, it is not relevant, since the number will be non-negative.

MATLAB: Can someone help with the code? (about factores primes)

Trivial.

factor(600861475143)
ans =
   3   3   3   3   60943  121721
max(factor(600861475143))
ans =
   121721

Ok, I suppose you are not allowed to use factor. But, perhaps you need to look at the actual factors of that number, and think about why your code failed.

What happens when there are repeated factors? You will find the first factor of 3 there, but then you increment prime. So you never found those second, third, or fourth factors of 3. At the very least, once you find a prime factor, you need to see if it is a multiple factor of your number.

As bad, what would have happened with your code had your teacher given you this number instead: 600861475147

This last number is prime. How many iterations of your loop would be needed to identify that it is indeed prime? 600 BILLION iterations of that loop (essentially 600 billion trial divides) would be needed before it would give up. (A modulus computation is essentially equivalent to a division.)

The point is, do you need to test for a factor that is larger than sqrt(n)? Think about it. For any number n, how many prime factors can the number n have that are larger than sqrt(n)?

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Related Solutions

MATLAB: How do you enter the command for a cube root

MATLAB: Can someone help with the code? (about factores primes)

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