Turning a sequence of operations into a function

I have a sequence of operations that attempts to calculate, whether there is an increase or a decrease in the next step, in comparison with the previous element of a matrix f:

f = [5 6 8 1 2  10 1 0 9 4 6 4]
f1 = [0]
k = 2
for i = 1:length(f)-1
if f(i+1) > f(i)
f1(k) = 1
else
f1(k) = 0
end
k = k+1
end

The code gives correct results.

How can I generalize the code into a function?

Answer 1

[Jan]

Start with simplifying the code:

• k is i+1 in all cases, so omit k and use i+1.
• Pre-allocate f1 by zeros() to avoid n iterative growing.
• This is equivalent:

% Version 1:
if condition
   a(k) = 1;
else
   a(k) = 0;
end

% Version 2:
a(k) = double(condition);

If a is preallocated as double, the casting by double() can be omitted.

f = [5 6 8 1 2 10 1 0 9 4 6 4];
f1 = zeros(size(f));
for i = 1:length(f)-1
    f1(i+1) = f(i+1) > f(i);
end

To convert this into a function:

f = [5 6 8 1 2 10 1 0 9 4 6 4];
f1 = compareWithNext(f)

function f1 = compareWithNext(f)
f1 = zeros(size(f));
for i = 1:length(f)-1
    f1(i+1) = f(i+1) > f(i);
end
end

Shorter versions:

f1 = [0, f(2:end) > f(1:end-1)]

% Or even simpler:
f1 = [0, diff(f) > 0];