How To Make Code Run Faster

What can I change about my code to make it run quicker/more efficiently? I would really appreciate it if things were listed one at a time, such as "change this one thing" or "change that one thing". I am trying to learn how to code more efficiently, but don't want to change my whole code, so changing one little thing here and there could really help me to learn this language better. Thank you!

 clear; clc;
 tic
 x=0:pi/100000:pi;
 y=sin(x);
 n=1;
 L=length(x);
 while n<L
     m(n,1)=x(n);
     m(n,2)=(y(n+1)-y(n))/(x(n+1)-x(n));
     n=n+1;
 end
 m(n,1)=x(n);
 m(n,2)=NaN;
 toc

Answer 1

[Stephen23]

1. The most important change you could make would be to preallocate the matrix m:

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html

2. You should also replace the while loop with a for loop, which is pretty easy as you know exactly how many iterations are required. In some low-level languages while loops are used very liberally, but in high-level MATLAB for loops are preferred (for simplicity, ease of debugging, etc).

3. The final step would be to realize that using a loop is an inefficient way to solve this problem anyway, and that using diff and rdivide would be simpler and faster.

[Bailey Smith]

To preallocate m, would it look something like this?

m=zeros(length(x))

[Stephen23]

L = numel(x);
m = zeros(L,2);

[Bailey Smith]

Thank you so much for the help!