MATLAB: What Dth stands for

Answer 1

It means that you have a variable named D and that you want the value of D to indicate which row number of H to access. If D had value 7 then you would want the "seventh" row. If it had value 8 then you would want the "eighth" row. If it had value 19, you would want the "nineteenth".

Explicit values such as 7 are "Cardinal" numbers -- numbers that tell you how much of something there is.

Designations such as "first" ("1st"), "second" ("2nd"), "third" ("3rd") are known as "Ordinal" numbers, and talk about the position of something. https://www.mathsisfun.com/numbers/cardinal-ordinal-nominal.html

So when refering to wanting to use the value stored in D as a position to look at, English would often use Ordinals -- most of which end in "th" in English. To refer to D as designating an Ordinal (position) English might then refer to the row . might also be written as or as . It means much the same thing as using the content of D as counting the number of rows that need to be dealt with (with the implication that the first (D-1) are not being paid attention to.)