How to generate a vector with the required values
180 次查看(过去 30 天)
显示 更早的评论
Dear all, I just noticed that if I create a vector like x=[.1:.1:.9] the result apparently is the same as creating it manually as x=[.1 .2 .3 .4 .5 .6 .7 .8 .9]; but it is not like that!
For example
>> x=[.1:.1:.9]
x =
0.1000 0.2000 0.3000 0.4000 0.5000 0.6000 0.7000 0.8000 0.9000
>> x(3)==.3
ans =
0
how can you explain that? And how can I be sure to create vectors with the required values???
FIY I'm using Matlab 2009b on a Unix environment. Cheers, -Luca
1 个评论
Jan
2011-2-15
Should we vote this question, because it is asked very frequently? Or should we not vote it, because the best answer would be not to ask the question at all? (sorry for this illogical formulation)
采纳的回答
Davide Ferraro
2011-2-15
The syntax:
x=[.1:.1:.9]
is creating a vector incrementally and due to Floating Point arithmetic approximation the obtained value may be different from the exact value from the vector definition.
Page, Troubleshooting Common Floating-Point Arithmetic Problems perfectly explains this with some possible approaches you may consider, especially if you are planning to do some "exact" comparison with ==.
0 个评论
更多回答(3 个)
Bruno Luong
2011-2-15
As Davide wrote, colon() operator will build the array by increment of the step (actually half incremental from both ends), and numerical errors will accumulate.
A more accurate way is using linspace(), which is computed by integer multiplication of the step.
a = linspace(0,1,11)
a == [0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1]
For what you want, probably the only way to get the exact value as command line is
a = eval('[0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1]')
3 个评论
Jan
2011-2-15
I assume the suggested EVAL method will increase the OP's misunderstanding of using floating point numbers in Matlab.
Aneeza Aneeza
2021-3-1
Create a table of conversions from m/h to ft/s. Start the mi/h column at 0 and end it at
100 mi/hr. Print 15 values in your table. (Note: 22 ft/s = 15 m/h)
0 个评论
另请参阅
类别
在 Help Center 和 File Exchange 中查找有关 Whos 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!