For example, I want to get a result like this. b=[1 diff(3)]=[1 0]. Not b=[1] .

differentiation of constant value is zero. But in matlab, diff(3)=[]; I want to get a vector which components are constant and zero. For example, I want to get a result like this. b=[1 diff(3)]=[1 0]. Not b=[1] How can I solve it?

[Iain]

What else can "3" be? - I mean can it be a vector or what?

Answer 1

[David Sanchez]

Do something like the following function:

function out=my_diff(in)
out = diff(in);
if isempty(out)
    out = 0;
end

Answer 2

[Jan]

diff() is not the "differentiation", but the "difference" of neighboring elements. As long as [3] does not have neighboring elements the result is empty, of course.

The "differentiation" is performed by the command gradient. But even with this [3] is not a well defined input: There is no slope between one point. Replying 0 is mathematically incorrect then.