Little truble with 'diff'

Hi everybody,

I'm trying to write the code for the function sing as you know there's an alternatively form:

Well here is the code that but gives me a little of trouble because for dimension

% sng(t) = (d/dt)*|t|

t = -10:10;

y = diff(abs(t));

figure(1);
plot(t,y); xlabel('t'); ylabel('sgn(t)');
%title('signum');
axis ([-10 10 -1.1 1.1])
grid on;

The problem is that when you use 'diff' with a 0 gives you this diff(0) = [], is an empty vector, any advice how can I fix or a way that 'diff' don't give me a empty space.

Thank you.

Answer 1

[Star Strider]

The MATLAB numeric diff function produces the difference of matrix or vector elements: [x(2)-x(1),x(3)-x(2),...] so if there is only one element in the argument you give it, it will return the empty array. It also returns a vector one element shorter than the argument vector. (The Symbolic Math Toolbox diff function calculates the symbolic derivative of its argument.)

If you want to take the numeric derivative, use the gradient function.

The derivative of 0 or any other constant will of course be 0.

[Luis Miguel López Santamaría]

Thank you very much :)

[Star Strider]

As always, my pleasure!