Signal's Fundamental Frequency is different from Plotted Signal I've been attempting to plot the following function using MATLAB:
$$
x(k)=\sum_{n=11}^{50} \sqrt{n} \sin (2n\pi k) +\sum_{n=1}^{40}\sqrt[3]{n} \sin (3n\pi k)
$$

Note that $k$ is a continuous variable.

The problem I am facing with MATLAB is when I plot it, I get a signal which has a fundamental period of 2 seconds, and not 1.5 seconds. 

Have a look below:


I've tried a higher sampling rate:


So, what is going on wrong? Why isn't the fundamental period 1.5Hz?
With $k$ a continuous variable, the frequencies of the sinusoids in the first sum are $f_n=n$, i.e. they are integers. The frequencies in the second sum are integer multiples of $\frac32$. The highest fundamental frequency of which all those frequencies are integer multiples is $f_0=\frac12$. The frequencies in the first sum are given by $2mf_0$ (with integer $m$), and the frequencies in the second sum are $3mf_0$. With a fundamental frequency of $f_0=\frac12$, the fundamental period is $T=2$, as observed by you.