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

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function [ absorption ] = solar_rad( nc,lat,t,I)

%Calculating absorbed solar radiation

% 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

for Insg=0.52*nc*Insd; %global radiation

Q_sun=Insd*(1-r)+0.97*Insg;

end

end

[absorption]=solar_rad(0,0,t,I);

Whenever I run it I get this error message:

Error in solar_rad (line 7)

for I=1:365;

Output argument "absorption" (and maybe others) not assigned during call to "\\fs-home-k\home-005\osp42f\My

Documents\MATLAB\Programmes\solar_rad.m>solar_rad".

##### 0 Comments

### Accepted Answer

Star Strider
on 12 Nov 2014

##### 2 Comments

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.

### More Answers (1)

Adam
on 12 Nov 2014

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;

##### 2 Comments

Adam
on 12 Nov 2014

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.

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