# I am trying to write a function but it will not work.

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Meghan on 12 Nov 2014
Commented: Star Strider on 12 Nov 2014
function [ absorption ] = solar_rad( nc,lat,t,I)
% Calculating the absorbed solar radiaiton as a function of time of
% day and year, cloud cover, and latitude, using a time step of one hour.
%BEGIN
for I=1:365;
for T=[0:24];
t=T*3600;
end
delta=-23.45*(pi/180)*cosd(2*pi)/365*(I+9); %Declination
S=1357+45*cosd((2*pi)/365)*(I); %Solar constant
for lat=0;
sinh=max(sind(lat)*sind(delta)+cosd(lat)*cosd(delta)*cosd((2*pi/86400)*(t+43200)));
m=1/sinh; %optical length
Cext=0.128-0.0253*(log(m)); %Extinction
end
for h=asin(max(sind(lat)*sind(delta)+cosd(lat)*cosd(delta)*cosd((2*pi)/86400)*(t+43200)));
i=(pi/2)-h; %angle of incidence
j=asin(0.75*sin(i)); %angle of reflection
r=0.5*abs((sin(i-j)^2/sin(i+j)^2)+(tan(i-j)^2)/(tan(i+j)^2)); %reflectance
end
end
for nc=0:100;
if h>0
Insd=S*(exp(-Cext*m))*(sin(h))*(1-(0.71*nc)); %direct incoming solar radiation at sea level
end
if h<=0
Insd=0;
end
Q_sun=Insd*(1-r)+0.97*Insg;
end
end
Whenever I run it I get this error message:
for I=1:365;
Output argument "absorption" (and maybe others) not assigned during call to "\\fs-home-k\home-005\osp42f\My

Star Strider on 12 Nov 2014
You donâ€™t have any variable named â€˜absorptionâ€™ on the left-hand side of any statement anywhere in your code for your â€˜solar_radâ€™ function. It has to have a variable by that specific name assigned somewhere in your code or it will not return any value for that variable.
Meghan on 12 Nov 2014
Yea I realised that and ended up fixing my code again! Now I'm just trying to figure out how to make a matrix joining I and T!
Star Strider on 12 Nov 2014
I don’t understand what you mean by ‘a matrix joining I and T’. ‘T’ and ‘I’ are indices.
Also, I don’t understand what you’re doing here:
cosd(2*pi)
since the trig functions ending with ‘d’ take their arguments in degrees. Those without take their arguments in radians. In any event, cos(2*pi) will always evaluate to 1, and cosd(2*pi) will always evaluate to 0.994.

Edited: Adam on 12 Nov 2014
r=0.5*abs((sin(i-j)^2/sin(i+j)^2)+(tan(i-j)^2)/(tan(i+j)^2));
That is your maths for 'r'. Without putting it into my Matlab it seems unlikely that will return an integer every time.
Q_sun=Insd(1-r)+0.97*Insg;
That is your maths indexing into Insd, which uses 'r'. Even if 'r' were an integer though the fact you use '1-r' means you will never end up with an integer index into your Insd array unless r == 0;
Meghan on 12 Nov 2014
Edited: Star Strider on 12 Nov 2014
I changed my code a little and now I get a new error message:
function [ absorption ] = solar_rad( nc,lat,t,I)
% Calculating the absorbed solar radiaiton as a function of time of
% day and year, cloud cover, and latitude, using a time step of one hour.
%BEGIN
for I=1:365;
for T=[0:24];
t=T*3600;
end
delta=-23.45*(pi/180)*cosd(2*pi)/365*(I+9); %Declination
S=1357+45*cosd((2*pi)/365)*(I); %Solar constant
for lat=0;
sinh=max(sind(lat)*sind(delta)+cosd(lat)*cosd(delta)*cosd((2*pi/86400)*(t+43200)));
m=1/sinh; %optical length
Cext=0.128-0.0253*(log(m)); %Extinction
end
for h=asin(max(sind(lat)*sind(delta)+cosd(lat)*cosd(delta)*cosd((2*pi)/86400)*(t+43200)));
i=(pi/2)-h; %angle of incidence
j=asin(0.75*sin(i)); %angle of reflection
r=0.5*abs((sin(i-j)^2/sin(i+j)^2)+(tan(i-j)^2)/(tan(i+j)^2)); %reflectance
end
end
for nc=0:100;
if h>0
Insd=S*(exp(-Cext*m))*(sin(h))*(1-(0.71*nc)); %direct incoming solar radiation at sea level
end
if h<=0
Insd=0;
end
Q_sun=Insd*(1-r)+0.97*Insg;
end
end
for I=1:365;
Output argument "absorption" (and maybe others) not assigned during call to "\\fs-home-k\home-005\osp42f\My
Any idea what I'm doing wrong? I've been trying to write this for 3 days!
Edited: Adam on 12 Nov 2014
You don't want a ';' at the end of that for loop line, although that maybe does no harm.
The error message tells you exactly what the problem is though despite perhaps erroneously pointing at that line.
You have stated there should be an output argument called 'absorption' yet you never create it.