How to assign new variables to an equation with set parameters?

Question

Kyle Lazaroff 2019-12-13

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/496535-how-to-assign-new-variables-to-an-equation-with-set-parameters

回答： Nishant Gupta 2019-12-16

So far this is the code i have for it, i need to split L_sun into 3 variables based off of values set by lambda.

close
clear
clc
r_d = 1.50e11; % distance from Earth to Sun
r_s = (1.39e9)/2; % radius of the sun 
fw =(r_s/r_d)^2;
t_s = 5800; % temp in kelvin
h = 6.626e-34; % in J*s
k_b = 1.381e-23; % in J/K
c = 2.998e8; % in m/s
syms lambda L_sun
lambda = (0.001:0.01:3)*1e-6;
L_sun = fw .* (2*pi*h*c.^2) ./ lambda.^5 .*...
    1./(exp((h*c)./(lambda*k_b*t_s)) -1);

every time i end up just assigning all of L_sun to the new variables instead of just the portions

uv = L_sun when lambda < 0.38e-6

vis = L_sun when 0.38e-6 < lambda < 0.78e_6

ir = L_sun when lambda > 0.78e-6

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Answer 1

Nishant Gupta 2019-12-16

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/496535-how-to-assign-new-variables-to-an-equation-with-set-parameters#answer_406556

You can modify the code as following:

syms lambda L_sun
lambda = (0.001:0.01:3)*1e-6;
j=1;
k=1;
l=1;
for i=1:300
    L_sun = fw .* (2*pi*h*c.^2) ./ lambda(i).^5 .* 1./(exp((h*c)./(lambda(i)*k_b*t_s)) -1);
                
 if (lambda(i) < 0.38e-6)
      uv(j) = L_sun;
      j = j + 1;
 elseif (lambda(i) > 0.38e-6) && (lambda(i) < 0.78e-6)
      vis(k) = L_sun;
      k = k+1;
   
 else 
      ir(l) = L_sun;
      l = l+1;
 end
end