# What does it mean to "% extract t and h(t) for time range 5.0<=t<=12.0" when "h=4.0+6.0​*t*10^-0.5​-(4*10^-0.​25)*cos(0.​75*pi*t)"?​; when

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Keith on 29 Sep 2022
Commented: Walter Roberson on 29 Sep 2022
Im not really sure what this means at all...
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### Answers (2)

Walter Roberson on 29 Sep 2022
One way:
Loop over the indices of the vector of t. At each point, make the "current" t equal to the t vector indexed at the current index value. Test the current t to see if it is in the desired range. If it is, then save the current t and save h indexed at the current index.
At the end, the saved t will be only the t in the desired range, and the saved h will be the corresponding h elements.
This is not what I would actually do myself: I would use logical indexing.
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Walter Roberson on 29 Sep 2022
What the phrase means is that you need to store all the t values that are in range into a variable, and you need to store the locations in h at the corresponding offset into a variable.

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Image Analyst on 29 Sep 2022
t is defined over some range, like 0 to 50 or whatever. Then the comment says they only want h values for t that is in the range 5-12. So you'd create a mask
t = linspace(0, 50, 51) % However you want it.
t = 1×51
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
h = 4.0 + 6.0 * t * 10^(-0.5) - 4 * 10^(-0.25) * cos(0.75 * pi * t)
h = 1×51
1.7506 7.4879 7.7947 8.1016 13.8388 11.8963 15.3842 18.8721 16.9296 22.6668 22.9737 23.2805 29.0178 27.0752 30.5631 34.0510 32.1085 37.8458 38.1526 38.4594 44.1967 42.2542 45.7421 49.2300 47.2874 53.0247 53.3315 53.6384 59.3756 57.4331
% Extract t and h(t) for time range 5.0<=t<=12.0"
% First make a mask
mask = (t >= 5) & (t <= 12)
mask = 1×51 logical array
0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
t2 = t(mask)
t2 = 1×8
5 6 7 8 9 10 11 12
h2 = h(mask)
h2 = 1×8
11.8963 15.3842 18.8721 16.9296 22.6668 22.9737 23.2805 29.0178
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