MATLAB: Comparing Data to find third set of data

aerospacedata importlifting lineread data

Here is part of my code that I am having problems with: The induced angle is currently 21 different values across the wing span (the alpha is currently fixed). I want to compare the angle_eff with values from excel files to obtain the coefficient of lift. I am able to match the angle_eff with the first column of excel data (alpha), but then I need it to take the corresponding lift coef. as it's value. Part of the excel data is provide below followed by the code. Can anyone help? If you wish to view the entire code just ask.
alpha  Lift Coef.
0  0
1  0.11
2  0.22
3  0.33
4  0.44
5  0.55
6  0.66
7  0.77
8  0.88
9  0.99
10  1.0685
angle_eff = (alpha - induced_angle);
figure(6)
plot(y,angle_eff)
%read data in 
val1 = xlsread('NACA0015.xlsx');
c1 = val1(:,1);
angle_eff_round = round(angle_eff);
display(c1)
c2 = val1(:,2);
%display(angle_eff_round)
num = length(c1);
for i = 1:num
  cl_new = ismember(c1,angle_eff_round);
  %if cl_new == true
    %end
end
%figure(7) %plot(y,cl_new)

Best Answer

You should abstract your problem into a mathematical or MATLAB programming problem. Don't let the details of your application obscure the problem. I'll take a guess using the following example:
A=[0  0
1  0.11
2  0.22
3  0.33
4  0.44
5  0.55
6  0.66
7  0.77
8  0.88
9  0.99
10  1.0685];
c=1:2:10
index=ismember(A(:,1),c)
SelectedData=A(index,2)
c =
     1     3     5     7     9
index =
     0
     1
     0
     1
     0
     1
     0
     1
     0
     1
     0
SelectedData =
    0.1100
    0.3300
    0.5500
    0.7700
    0.9900
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