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onrammp exercise 14.2 stellar motion part 2, task 6 movaway

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Darnell Gawdin
Darnell Gawdin 2020-1-3
Locked: DGM 2024-7-17
For task 6 I don't understand how matlab connects starname to a particular graph.
Also I'm not sure how this piece of code works...
"movaway = starnames(speed < 0) "
how does this line of code use a variable that is in a loop before this line of code?
Sorry in advance if this is an obvious question.
Task 1
[sHa,idx] = min(spectra);
lambdaHa = lambda(idx);
z = lambdaHa/656.28 - 1;
speed = z*299792.458
Tasks 2 - 4
for c = 1:7
s = spectra(:,c);
if speed(c) >= 0
loglog(lambda,s,"--")
else
loglog(lambda,s,"LineWidth",3)
end
hold on
end
hold off
Task 5
legend(starnames)
Task 6
movaway = starnames(speed < 0)
  1 个评论
Nikita
Nikita 2024-2-12
Add an if statement to the for loop body. If speed(v) is less than or equal to 0, create a plot of s against lambda using a dashed line (--).
Add the command hold on between the two end keywords so that you only create one plot.

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采纳的回答

KALYAN ACHARJYA
KALYAN ACHARJYA 2020-1-3
编辑：KALYAN ACHARJYA 2020-1-3
See the example, lets suppose starnames is variable having all types of numbers
starnames=[-2 3 45 7 2 0 -4 5 7 7 6 9];
speed=[2 3 -4 5 6 7 8 0 5 2 -30] ; % Just random example
## speed<0 is an conditional assignment, its return a logical array (with 0 & 1), when condition true, its 1, otherwise 0
>> speed < 0
ans =
1×11 logical array
0 0 1 0 0 0 0 0 0 0 1
## starnames(speed < 0) return an array, where the 1 presence in the above logical array
>> movaway = starnames(speed < 0)
movaway =
45 6
This is just an example to understand the issue (This approach is good way for efficient code, conditional & array indexing)
  1 个评论
Darnell Gawdin
Darnell Gawdin 2020-1-3
Thank you for your time and expertise to answer this question. I see how it works now.

更多回答（1 个）

Bongani Tavengwa
Bongani Tavengwa 2020-6-5
编辑：DGM 2023-2-22
Task
Add an if statement to the for loop body. If speed(c) is less than or equal to 0, create a loglog plot of s against lambda using a dashed line (--).
After the if statement, add the command hold on so that only one plot is created.
for c = 1:7
s = spectra(:,c);
if speed(c) >= 0
loglog(lambda,s,"--")
else
loglog(lambda,s,"LineWidth",3)
end
hold on
end
please help me where do i go wrong
  9 个评论
显示 7更早的评论
Narmadha
Narmadha 2023-9-9
Add an else statement. If speed(v) is greater than 0, create a plot of s against lambda using a line width of 3.
After the for loop, enter hold off.

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