I want to calculate c with this exemple.

clc
clear all;  
close all;
% The latitude of the location.
lat=input('Give lattitudelta du lieu');


for i=1:1:12
    %DECLINATION
    Days=[17 47 75 105 135 162 198 228 258 288 318 344];
    delta(i)=23.45*(pi/180)*sin(pi/180*(284+Nj(i))*360/365)
    phir=lat*ones(1,12)*pi/180
%     sunrise and sunset time calculation
    du(i)=(2/15)*(180/pi)*acos((-tan(delta(i))).*(tan(phir(i))) );
    dur(i)=(24/pi)*du(i);
    sunrise(i)=12-180/pi*acos(-tan(phir(i))*tan(delta(i)))/15;
    sunset(i)=12+180/pi*acos(-tan(phir(i))*tan(delta(i)))/15;
    c=sunrise(i):0.5:sunset(i)
end

C is a matrix that contains for each day a vector that goes from sunrise to sunset with a step of 0.5. as illustrated in the figure below

[Torsten]

Is

sunset(i) - sunrise(i) 

equal for all i and an integer number ? If not, C cannot be generated.

[Mathieu NOE]

Unrecognized function or variable 'Nj'.

Error in matlabhelp1 (line 11)

delta(i)=23.45*(pi/180)*sin(pi/180*(284+Nj(i))*360/365)

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^