You vary as a function of time

You vary as a function of time
You wake up in the morning and you always feel fine
But in the evening when the sun sets you begin to lose your mind
You vary as a function of time

Your mood sets a sinusoidal path
At lunchtime all I have to do is smile to see you laugh
but as your temper worsens I depict it on a graph
and your mood takes a sinusoidal path

There's a formula for your personality
y = (7n + 4) / 16t
Where t's the time and n is your proximity to me
There's a formula for your personality