Invorrect number of answers

Question

Sarah Kneer 2020-12-23

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https://ww2.mathworks.cn/matlabcentral/answers/701152-invorrect-number-of-answers

评论： Image Analyst 2020-12-23

For this script I'm meant to use each value of d - 3 values - with each value of h - 24 answers - hence I should have 72 answers, but I only have 24 answers. Please help:

phi = 53;
h = 1/24:1/24:1;
d = 100:100:365;
for i = 1:1:length(d)
    delta(i) = -23.45 * cosd((360/365) * (d(i)+10));
    for j = 1:1:length(h)
    h_a(j) = 360 * (h(j)-0.5);
    alpha(j) = asind(((sind(phi) * sind(delta(i))) + (cosd(phi) * cosd(delta(i)) * cosd(h_a(j)))));
    theta(j) = 90 - alpha(j);
    end
    if h <= 0.5
    beta(j) = -acosd((((sind(delta(i)) * cosd(phi)) - (cosd(h_a(j)) * cosd(delta(i)) * sind(phi)))/sind(theta(j))));
    else
    beta(j) = acosd((((sind(delta(i)) * cosd(phi)) - (cosd(h_a(j)) * cosd(delta(i)) * sind(phi)))/sind(theta(j))));
    end
end

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Answer 1

Walter Roberson 2020-12-23

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After your for for j loop, which ends before the if, j will have a value that is the last value assigned to it in the loop; for j=1:1:length(h) will leave j=length(h) after the loop. That is a single value, 24, so you are always writing to beta(24) so you are only ever getting one answer.

You should move the assignment inside the for loop, and you should assign to beta(i,j)

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Sarah Kneer 2020-12-23

Okay, now it’s working, thank you very much

Image Analyst 2020-12-23

Can you please "Accept" an anwer, and/or Vote for them, to give those who helped you "reputation points"? Thanks in advance.

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Answer 2

Cris LaPierre 2020-12-23

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You are only capturing 1/3 of your data, then. This is because your outer for loop is always overwriting the previous result. This leaves you with just the values calculated in the last loop only.

To see how to capture all values, look at this example from the documentation.

Also, your if statement will always be false with the given criteria. This is because h is a vector, and the result of your conditional is mixed (~half true, half false). Perhaps you meant to include this inside your inner for loop? That would make more sense, since you index beta using your loop counter j. For your conditional, use h(j).