Subscript indices problem with a for loop

Question

Camran Purewal 2017-3-15

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/330053-subscript-indices-problem-with-a-for-loop

编辑： Jan 2017-3-15

Hello, I am having problems creating a for loop to calculate and store temperatures in the various sections of the atmosphere, with the following code I get the error "Subscript indices must either be real positive integer or logicals":

Altitude = 0:1:100000; Temperature 1 = 288.15; L0 = -0.0065;

for i = 1:11001 Altitude = i -1; Temperature(Altitude) = Temperature1 + (L0*Altitude); end

Thank you.

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Answer 1

Jan 2017-3-15

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https://ww2.mathworks.cn/matlabcentral/answers/330053-subscript-indices-problem-with-a-for-loop#answer_258893

编辑：Jan 2017-3-15

在 MATLAB Online 中打开

With your code in the first iteration tis happens:

Temperature(0) = Temperature1 + (L0 * Altitude);

but 0 is not a valid index. USe this instead:

Temperature1 = 288.15;
L0           = -0.0065;
Temperature  = zeros(1, 11001);  % Pre-allocate!!!
for k = 1:11001
  Temperature(i) = Temperature1 + (L0 * (i-1));
end

Or shorter without the loop:

Temperature = Temperature1 + L0 * (0:11000);

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Answer 2

Alexandra Harkai 2017-3-15

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https://ww2.mathworks.cn/matlabcentral/answers/330053-subscript-indices-problem-with-a-for-loop#answer_258894

在 MATLAB Online 中打开

Altitude is 0 in the first loop, which is not a valid index in this case.

It is suspicious though that you assign a numerical array to Altitude, then later it gets overwritten by i-1.

This also doesn't look OK, you should get an error:

Temperature 1 = 288.15;

Overall it seems you are using a loop for something that doesn't require a loop: multiplying a vector with a scalar and then adding another scalar to it. You can just write it like so:

Temperature = Temperature1 + (L0 * 0:11000);