For Loop "Array indices must be positive integers or logical values"

Good Morning all,

I have the below statement and its not working when i swith signs and i dont understand why. Appreciate the help!

THIS WORKS

for k = 2:nmr

if a(k) > a(k-1) & a(k-1) > a(k-2) & b(k) < b(k-1) & b(k-1) < b(k-2)

result(k) = 1;

elseif result(k)==0

end

end

BUT Once i swith logical signs i get the matlab error

THIS DOESNT WORK

for k = 2:nmr

if a(k) < a(k-1) & a(k-1) < a(k-2) & b(k) > b(k-1) & b(k-1) > b(k-2)

result(k) = 1;

elseif result(k)==0

end

end

Answer 1

[David Hill]

matlab starts indexing at 1, you cannot index into an array at 0

for k = 2:nmr
    if a(k) < a(k-1) & a(k-1) < a(k-2) & b(k) > b(k-1) & b(k-1) > b(k-2)

b(k-2) is b(0) when k==2 which cannot happen, matlab will error.

[IDN]

Got it, thanks. So how can i have matlab start running after K==3 ?

[IDN]

Got it thanks!

[David Hill]

You could start your loop at 3.

for k = 3:nmr

or do something about the b(k-2)

for k = 2:nmr
    if a(k) < a(k-1) & a(k-1) < a(max(1,k-2)) & b(k) > b(k-1) & b(k-1) > b(max(1,k-2))

Answer 2

[Image Analyst]

See the FAQ:

https://matlab.fandom.com/wiki/FAQ#%22Subscript_indices_must_either_be_real_positive_integers_or_logicals.%22