MHB Plotting y=x^1/3 - Why Different Results?

  • Thread starter Thread starter Yankel
  • Start date Start date
  • Tags Tags
    Plotting
Yankel
Messages
390
Reaction score
0
Dear all,

I was using the computer in order to plot the graph of

\[y=x^{\frac{1}{3}}=\sqrt[3]{x}\]

and two different plotters gave two different results. I don't understand why. Can you kindly explain ?

The results are:

View attachment 8447

View attachment 8448

Thank you !
 

Attachments

  • plot 1.PNG
    plot 1.PNG
    1.4 KB · Views: 110
  • plot 2.PNG
    plot 2.PNG
    2.3 KB · Views: 114
Mathematics news on Phys.org
First, of course, those are the same for x> 0 just scaled differently. As for x< 0 it looks like the first plotter is using logarithms "unthinkingly" to calculate fractional powers and the logarithm of negative numbers do not exist.
 
Generally $x^{1/3}$ is considered to be undefined for negative $x$, although some books do effectively define it as $-(-x)^{1/3}$.

Reasons are:
  1. The power identity $a^{b\cdot c}=(a^b)^c$ breaks down. Consider:
    $$-1 = (-1)^{2/3\cdot 3/2} \ne ((-1)^{2/3})^{3/2} = 1^{3/2} = 1$$
  2. Calculators evaluate it as $x^{0.33333}$, which is undefined for negative x.
    Note that we can only define something like $x^{1/3}$ for negative x if the power is a fraction with an odd number in the denominator, but that is generally not supported by calculators.
 
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. In Dirac’s Principles of Quantum Mechanics published in 1930 he introduced a “convenient notation” he referred to as a “delta function” which he treated as a continuum analog to the discrete Kronecker delta. The Kronecker delta is simply the indexed components of the identity operator in matrix algebra Source: https://www.physicsforums.com/insights/what-exactly-is-diracs-delta-function/ by...
Fermat's Last Theorem has long been one of the most famous mathematical problems, and is now one of the most famous theorems. It simply states that the equation $$ a^n+b^n=c^n $$ has no solutions with positive integers if ##n>2.## It was named after Pierre de Fermat (1607-1665). The problem itself stems from the book Arithmetica by Diophantus of Alexandria. It gained popularity because Fermat noted in his copy "Cubum autem in duos cubos, aut quadratoquadratum in duos quadratoquadratos, et...
I'm interested to know whether the equation $$1 = 2 - \frac{1}{2 - \frac{1}{2 - \cdots}}$$ is true or not. It can be shown easily that if the continued fraction converges, it cannot converge to anything else than 1. It seems that if the continued fraction converges, the convergence is very slow. The apparent slowness of the convergence makes it difficult to estimate the presence of true convergence numerically. At the moment I don't know whether this converges or not.
Back
Top