Why do we usually use M,N,P to indicate dimensions?

taken to indicate the dimension of the array m, n, p. the meaning of these letters I guess that m - main n -??? p - page?

Answer 1

[Paulo Silva]

They are just variables when used like this:

[m,n,p] = size(rand(2,3,4))

m holds the first dimension (the number of rows)
n holds the second dimension (the number of columns)
p holds the third dimension of the array, think about it like the number of pages

[Vitaly]

thank you, but I would like to know why m,n,p instead of r,c,p ...

[Matt Tearle]

abcdefghijklMNoPqrs...

That's it. Just consecutive letters typically used to denote integers. (O is skipped due to its similarity to 0).

[Paulo Silva]

just variables, no particular meaning, use the variables you like the most

[Walter Roberson]

Historical habit in mathematics, just like using the beginning of the alphabet to represent constants and using the end of the alphabet to represent variables.

Answer 2

[karthika]

m and p gives the number of rows and columns

[Vitaly]

as I know m and n gives the number of rows and columns, is any advantage to use p for columns due the best perfomance?

[Walter Roberson]

No. The programming language doesn't care which variable name you use, but you will lose efficiency from people reading your code and attempting to figure out what your names mean. If you are going to use non-traditional names, use names that are self-explanatory.