I want to create a function that repeats on an annual cycle (i.e. time is a vector of $1$ to $365$), that has $2$ peaks of different magnitudes - one approx a third of the year and the second approx two thirds of the year. The mean of the cycle is ~$450$, with the $y$-limits being ~$100-800$. The value at the beginning of the year should be the minimum value.
With the help of a much more mathematically-minded friend, I've managed to get the following:
$\text{MeanValue} + 250\left(\sin\left(\frac{0.2164}{2\pi}\left(\text{time}-55\right)\right)+\left(\sin\left(\frac{0.2164\cdot0.5}{2\pi}\left(\text{time}-55\right)\right)\right)\right)$
where MeanValue is $450$ and time is the vector of $1$ to $365$.
However, although this seems to show the correct pattern over a small number of years, after $1000$ years, the value at the end of the year is not the minimum value, but ~$700$, implying the whole cycle seems to be about half a phase out by then. What am I missing to make this repeat in the way I want?