Indexing Exceeds number of array elements

et=4; dn1=1:61;
for ii=length(dn1)
r(ii)=(et+((dn1(ii+1)-dn1(ii))))./((dn1(ii)-(dn1(ii-1)))+et);
end

Index exceeds the number of array elements. Index must not exceed 61.

Answer 1

[Image Analyst]

Look at your indexes - they go from ii-1 to ii+1 so ii can only go from 2 to length(dn)-1

et=4;
dn1=1:61;
for ii = 2 : length(dn1)-1
    r(ii) = (et+((dn1(ii+1)-dn1(ii))))./((dn1(ii)-(dn1(ii-1)))+et);
end

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