How to get the relsults in different matrix after for loop

Question

Shubham Mohan Tatpalliwar 2019-1-22

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/440865-how-to-get-the-relsults-in-different-matrix-after-for-loop

关闭： MATLAB Answer Bot 2021-8-20

Hello all,

I am working on a engine in which i want a result at different rpm... let i be the different rpm and A be the fuel consumption

B and C as the factor for calculating them.

At the end i want to have 3 matrices

A1 when i = 1

A2 when i = 2

A3 when i = 3

B=[1 1; 1 1]
C=[2 2;2 2]
for i=1:3
    A= B*i+C*i
end

What should i add up in this program to get the desired result

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Stephen23 2019-1-22

编辑：Stephen23 2019-1-22

Using numbered variables is a sign that you are doing something wrong.

Putting numbers into variable names like that treats those numbers as pseudo-indices, which are slow, complex, and buggy to work with. It is much simpler to use real indices, which are neat, efficient, and very easy to debug. Unlike what you are trying to do.

Read this to know more:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

For example, you could easily use a cell array:

A = cell(1,3);
for k = 1:3
    A{k} =  B*k + C*k;
end

but probably the best solution would be to learn how to use arrays and write vectorized code. Then you can trivially avoid the loop entirely and write simpler, more efficient code:

V = reshape(1:3,1,1,[]);
A = B.*V + C.*V

请先登录，再回答此问题。

Answer 1

Walter Roberson 2019-1-22

3
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/440865-how-to-get-the-relsults-in-different-matrix-after-for-loop#answer_357455

We recommend against that firmly.

evils of eval

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Stephen23 2019-1-22

编辑：Stephen23 2019-1-22

"why is it not recommended... can u please explain"

Did you try reading the link that Walter Roberson gave you?

" right now i am new to matlab n wanna learn "

Is that why you accepted an answer which shows you how to write slow, complex, inefficient, obfuscated, hard-to-debug MATLAB code? If you want to learn, try reading the link that Walter Roberson gave you.

Answer 2

StefBu 2019-1-22

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/440865-how-to-get-the-relsults-in-different-matrix-after-for-loop#answer_357457

编辑：StefBu 2019-1-22

Hi if you really want to use eval,try this code:

for i=1:3
    tempName = ['A', num2str(i)];
    eval([tempName '= B*i +C*i;']);
end

Greetings

Stefan

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Stephen23 2019-1-22

编辑：Stephen23 2019-1-22

Or you could use this opportunity to learn why this is a really slow, complex, inefficient, buggy way to write code. For example, by reading the MATLAB documenation, which clearly states: "A frequent use of the eval function is to create sets of variables such as A1, A2, ..., An, but this approach does not use the array processing power of MATLAB and is not recommended. The preferred method is to store related data in a single array."

source: https://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

Beginners would improve their MATLAB code quite a lot by following the advice in the MATLAB documentation. Read more here:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval