Why do i get this error when i run the code?

Hello there friends i tried to run this code in matlab r2021b

dn=1:1:365;
x=(360/365*(dn+284));
sdelta=23.45*(sind(x)*pi/180);
L=(0:20:80);
k=(0:0.5:24);
lamda=15*(12-k);
solar_altitude=asind(sind(sdelta)*sind(L)+cosd(sdelta)*cosd(L)*cosd(lamda));

but the system shows this error ...can anybody help me out.Thank you.

Error using *

Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches

the number of rows in the second matrix. To perform elementwise multiplication, use '.*'.

Error in p2 (line 43)

solar_altitude=asind(sind(sdelta)*sind(L)+cosd(sdelta)*cosd(L)*cosd(lamda));

Answer 1

[Walter Roberson]

dn=1:1:365;
x=(360/365*(dn+284));
sdelta=23.45*(sind(x)*pi/180);
L=(0:20:80);
k=(0:0.5:24);
lamda=15*(12-k);
whos

  Name        Size             Bytes  Class     Attributes

  L           1x5                 40  double              
  dn          1x365             2920  double              
  k           1x49               392  double              
  lamda       1x49               392  double              
  sdelta      1x365             2920  double              
  x           1x365             2920  double              

solar_altitude=asind(sind(sdelta)*sind(L)+cosd(sdelta)*cosd(L)*cosd(lamda));

Error using *
Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of rows in the second matrix. To perform elementwise multiplication, use '.*'.

sdeleta is 1 x 365 so sind(sdelta) is also 1 x 365

L is 1 x 5 so sind(L) is 1 x 5

(1 x 365) * (1 x 5) is an invalid operation.

It looks to me as if you want a result that is per-latitude and per-day -- so a 2D result. For long term graphing purposes it is probably easiest to have connect all of the days for a particular latitude, so you probably want one line per latitude (ignoring the other factors for now), so you should arrange for sdelta to be a column.

[prem kumar]

friend actually the instruction given to me is as follows:

Write a Matlab program to calculate solar altitude, at L = 0, 20, 40, 60, 80 deg for ( k = 0.5, 1, 1.5, 2, 2.5 … 24 i.e half-hour interval) for dn = 100.

Plot solar altitude, versus solar time, k at L = 0, 20, 40, 60, 80deg on a single graph.

[Walter Roberson]

dn = (1:1:365).';
x=(360/365*(dn+284));
sdelta=23.45*(sind(x)*pi/180);
L=(0:20:80);
k=(0:0.5:24);
lamda=15*(12-k);
whos

  Name          Size            Bytes  Class     Attributes

  L             1x5                40  double              
  dn          365x1              2920  double              
  k             1x49              392  double              
  lamda         1x49              392  double              
  sdelta      365x1              2920  double              
  x           365x1              2920  double              

part1 = sind(sdelta)*sind(L); size(part1)

ans = 1×2

365 5

part2a = cosd(sdelta)*cosd(L); size(part2a)

ans = 1×2

365 5

part2 = part2a * cosd(lamda); size(part2)

Error using *
Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of rows in the second matrix. To perform elementwise multiplication, use '.*'.

solar_altitude=asind(part1 + part2);

So you now have two pieces that are 365 x 5, and you want to somehow relate them to lamda which is 1 x 49.

What size of output are you hoping for?

... Because at the moment it looks to me as if k has to do with solar time in minutes, which you would normally expect to be used to refine the day number to produce an "every 30 minutes of every day" result (one continuous vector) for each different latitude location, not a (days) by (latitudes) by (30-minute-intervals) result.

[prem kumar]

but friend in the instruction they didnt specify k is in minutes or hours they only specified for lamda as where the hour angle, based on solar time k..Also its for dn=100 and they didnt specify the lattitude in the question unfortunately...i also try to search some related equation for this type of solar related problems they used lattitude at a specified location in those equations..as per the size i do not mind any output size to be honest..so it means i have to change my k value into minutes in order to get 1x365 but it is only for a day though.

[Walter Roberson]

dn = (1:1/24:365).';
x=(360/365*(dn+284));
sdelta=23.45*(sind(x)*pi/180);
L=(0:20:80);
k = mod(dn, 1) * 24;
lamda=15*(12-k);
whos

  Name           Size            Bytes  Class     Attributes

  L              1x5                40  double              
  dn          8737x1             69896  double              
  k           8737x1             69896  double              
  lamda       8737x1             69896  double              
  sdelta      8737x1             69896  double              
  x           8737x1             69896  double              

part1 = sind(sdelta)*sind(L); size(part1)

ans = 1×2

8737 5

part2a = cosd(sdelta)*cosd(L); size(part2a)

ans = 1×2

8737 5

part2 = part2a .* cosd(lamda); size(part2)

ans = 1×2

8737 5

solar_altitude = asind(part1 + part2);

whos

  Name                   Size             Bytes  Class     Attributes

  L                      1x5                 40  double              
  ans                    1x2                 16  double              
  dn                  8737x1              69896  double              
  k                   8737x1              69896  double              
  lamda               8737x1              69896  double              
  part1               8737x5             349480  double              
  part2               8737x5             349480  double              
  part2a              8737x5             349480  double              
  sdelta              8737x1              69896  double              
  solar_altitude      8737x5             349480  double              
  x                   8737x1              69896  double              

plot(dn, solar_altitude); legend(string(L))

plot(dn(1:200), solar_altitude(1:200,:)); legend(string(L))

Perhaps the equations are not correct when dn is fractional ?

[prem kumar]

but i looked at solar radiation conference book this is the same equation he used...but is it possible if to make like only for the hundredth day dn=100 instead of dn=1:200?