How to create a matrices using while loop?

Question

Teb Keb 2022-2-14

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1649210-how-to-create-a-matrices-using-while-loop

评论： Teb Keb 2022-2-15

Hi,

I am creating a 6x3 matrices using while loop with the variable increments by 1 (increment=1:1:5). My codes seems to work but it shows one row of the result at a time, instead of creating a matrices with 6 rows and 3 columns in the command window.

>> r=0.1;
y=2.5;
i=0;
while i<=5
    i=i+1;
    dis(i)=r.*sin(y.*i);
    tim(i)=dis(i)*2;
    a=[i dis(i) tim(i)]
end
a =
    1.0000    0.0598    0.1197
a =
    2.0000   -0.0959   -0.1918
a =
    3.0000    0.0938    0.1876
a =
    4.0000   -0.0544   -0.1088
a =
    5.0000   -0.0066   -0.0133
a =
    6.0000    0.0650    0.1301

Instead of having my answer a=, how do i put them into matrix array (6x3) as the increments increases by 1 until it hits 5 using while loop only?

Thank you,

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Answer 1

Stephen23 2022-2-14

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1649210-how-to-create-a-matrices-using-while-loop#answer_895345

在 MATLAB Online 中打开

r = 0.1;
y = 2.5;
i = 0;
a = []; % <---
while i<=5
    i=i+1;
    dis = r.*sin(y.*i);
    tim = dis*2;
    a = [a;i,dis,tim];
    %    ^^
end
display(a)
a = 6×3
    1.0000    0.0598    0.1197
    2.0000   -0.0959   -0.1918
    3.0000    0.0938    0.1876
    4.0000   -0.0544   -0.1088
    5.0000   -0.0066   -0.0133
    6.0000    0.0650    0.1301

But this is not an efficient use of MATLAB. A much better approach is to use a FOR loop with preallocated array, e.g.:

N = 6;
a = nan(N,3);
for k = 1:N
    dis = r.*sin(y.*k);
    tim = dis*2;
    a(k,:) = [k,dis,tim];
end
display(a)
a = 6×3
    1.0000    0.0598    0.1197
    2.0000   -0.0959   -0.1918
    3.0000    0.0938    0.1876
    4.0000   -0.0544   -0.1088
    5.0000   -0.0066   -0.0133
    6.0000    0.0650    0.1301

Note that using a loop is not required, the simpler MATLAB approach would be something like this:

vec = 1:N;
dis = r.*sin(y.*vec);
tim = dis*2;
a = [vec;dis;tim].'
a = 6×3
    1.0000    0.0598    0.1197
    2.0000   -0.0959   -0.1918
    3.0000    0.0938    0.1876
    4.0000   -0.0544   -0.1088
    5.0000   -0.0066   -0.0133
    6.0000    0.0650    0.1301