Why is this generating a numerical array and not an array of cells?

Why does the following loop generate slope as the result of diff() function? Instead or a cell array with the desired text?

for i=1:length(Temp_F)
   if diff(Temp_F(i))>0
       slope(i)='Rising'
   elseif diff(Temp_F(i))<0 
       slope(i)='Falling'
   end
 end   

[Stephen23]

diff(Temp_F(i))

What do you expect the difference of one number to be?

Answer 1

[KSSV]

REad about the function diff. It needs an array with atleast 1x2 dimensions. You are giving only one number as input. So diff gives you an empty matrix.

diff(1)

ans =

     []

diff(rand)

ans =

     []

diff(rand(1,2))

ans = 0.0347

diff(rand(2,1))

ans = 0.5240

So you have to modify your code like below:

diff_Temp_F = diff(Temp_F) ;  % I assume Temp_F is a vector 
N = length(Tmp_F) ; 
slope = cell(N,1) ; 

for i=1:length(Temp_F)-1
   if diff_Temp_F(i) > 0
       slope{i}='Rising'
   elseif diff_Temp_F(i) < 0
       slope{i}='Falling'
   end
 end   

[Image Analyst]

I believe you could also use strings instead of character arrays and then use parentheses instead of braces

slope(i) = "Rising"; % Use double quotes instead of single quotes.