# Meaning/name of mid placed dot at end of equation.

#### RBeast

##### New member
Hello,

I am studying a number if equations relating to engineering and have no idea if this is the right forum I did look around a little bit and attempt to place it correctly. Please forgive me this is the wrong place.

What is the function of the dot in this equation? Just the name of its function would help.

Many thanks!

#### tkhunny

##### Moderator
Staff member
It appears to me that you have encountered the end of a sentence.

Since you have provided no additional context, I can't be certain.

#### RBeast

##### New member
It appears to me that you have encountered the end of a sentence.

Since you have provided no additional context, I can't be certain.

Yes, I imagine it looks that way. I had intended to add more when my phone battery barked at me.

The equation is from the Catenary page on Wikipedia.
https://en.m.wikipedia.org/wiki/Catenary

There are other equations on that page using similar notation.

I entered the equation as written in Grapher and observed the correct result. Removing the period gives a different result.

If I knew better how to describe it, I might have figured it out. Lol

#### RBeast

##### New member
It appears to me that you have encountered the end of a sentence.

Since you have provided no additional context, I can't be certain.

It sure looks like it might be that simple. I thought it was some sort of differentiation shorthand, but it only appears when the equation is the end of a sentence. Since an equation is usually spaced below to be in its own space, it seems like added typograghy symbols would be left out. That said, a comma doesn’t look out of place in a stream of equations.

Perhaps a case of thinking too hard. Lol

#### barrick

##### New member
Yes, I imagine it looks that way. I had intended to add more when my phone battery barked at me.

The equation is from the Catenary page on Wikipedia.
https://en.m.wikipedia.org/wiki/Catenary

There are other equations on that page using similar notation.

I entered the equation as written in Grapher and observed the correct result. Removing the period gives a different result.

If I knew better how to describe it, I might have figured it out. Lol

$$\displaystyle \displaystyle\frac{d\phi}{ds}=\frac{\cos^2{\phi}}{a}$$

which is what you get if you simply ignore the dot.

#### tkhunny

##### Moderator
Staff member
The punctuation apppears to be consistent throughout.

Note this one: $$\displaystyle \dfrac{dy}{dx}=\dfrac{s}{a}$$,

This is not the END of a sentence, but clearly intended to be part of a sentence.

Read each one carefully. See if the sentence ends or continues. Read above and below. Decide where you would provide what punctuation.

#### stapel

##### Super Moderator
Staff member
Odd. The coding for the expression actually includes the dot as part of the math:

Code:
{\displaystyle \tan \varphi ={\frac {s}{a}}\,.}
They intentionally added a space after the fraction, and then included the "dot", so it wouldn't appear to have been meant as a sentence-ending full-stop. Sloppiness on the authors' part, maybe...?

#### mmm4444bot

##### Super Moderator
Staff member
I'm thinking the space before all of those periods and commas was an aesthetic decision, and they might have set the punctuation inside the LaTex code to prevent potential line breaks from orphaning the punctuation.