2

I am not looking for a formula to calculate the difference of two dates. I am looking for a notation to express the difference of two dates in a formula.

Is there a common way to do that? If not what would be a good way to express that?

I am thinking of something like this:

$t = diff(D_1, D_2)$

where $t \ge 0$ is the number of days and $D_1$ and $D_2$ are two dates.

elevendollar
  • 123
  • Maybe $\Delta_{D_1\to D_2} D$. That's what we used to do in Physics for moments and work. – Scientifica Mar 01 '15 at 12:22
  • What is the $D$ at the end? – elevendollar Mar 01 '15 at 18:38
  • You can see it as days. $\Delta_{D_1\to D_2}D=D(D_2)-D(D_1)=D_2-D_1$. In fact, sometimes what we're looking for isn't the difference of days but the difference of something else between these days. For example the temperature we have in something is $T_1$ in the day $D_1$ whereas $T_2$ is the temperature in the day $D_2$. Then $\Delta_{D_1\to D_2}T=T(D_2)-T(D_1)=T_2-T_1$. – Scientifica Mar 01 '15 at 21:34
  • But in fact the $D_1\to D_2$ should be under $\Delta D$ and $\Delta T$ just like for limits: $\lim\limits_{D_1\to D_2}$, but I failed to represent it here. – Scientifica Mar 01 '15 at 21:35
  • 1
    Thank you! That looks good. If you would like to formulate it as an answer I will accept it. – elevendollar Mar 02 '15 at 07:17
  • It doesn't really matters (at least for me xD). I'll formulate it as an answer. You're welcome! – Scientifica Mar 02 '15 at 15:17

1 Answers1

0

To express the difference of two quantities $Q_1$ and $Q_2$ in two different states $1$ and $2$ we use the $\mathop{\Delta{Q}}\limits_{1\to 2}=Q_2-Q_1$. Sometimes the states are clear so we just write $\Delta{Q}$ like with $\Delta{E}=(\Delta{m})c$. Sometimes we use $\mathop{\Delta{Q}}\limits_{Q_1\to Q_2}$ when we emphasize on the values. So in your case: $\mathop{\Delta{D}}\limits_{D_1\to D_2}=D_2-D_1$.

However, you should pay attention to what you make the difference for. If the difference is infinitesimally small, we use instead $d$ or $\delta$ like for $v=\frac{dx}{dt}$.

Scientifica
  • 8,781