Using loop to sum value of an array and summation

Question

DoinK 2023-6-10

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1981059-using-loop-to-sum-value-of-an-array-and-summation

编辑： Stephen23 2023-6-11

采纳的回答： Alan Stevens

在 MATLAB Online 中打开

I have 2000 row vector which each array has 1008 column.

I need to sum every array to only 4 column, so every 252 item, i sum it, so the array now has 4 column.

For example, i use only 1 row vector which has 12 column and every 3 item i sum it:

J=[1 2 3 4 5 6 1 2 3 4 5 6];
for i=1:length(J)
    a=sum(J(1:3));
    b=sum(J(4:6));
    c=sum(J(7:9));
    d=sum(J(10:12));
end
p0=[a b c d]
p0 = 1×4
     6    15     6    15

After that, i have to do summation:

for j=1:4
    f=j*p0(j);
    h(j)= sum(f);
end
h
h = 1×4
     6    30    18    60

I can call 'h' too like h(3) is 18.

I can do it for small input like this, how to code for big vector?

How to summation up to 2000 vector and can call every 'h'?

May i know, summation mostly start with 0, but looping with (for) command cannot do it, ''Array indices must be positive integers or logical values."

Is there any command to use to start with 0?

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Stephen23 2023-6-10

编辑：Stephen23 2023-6-11

在 MATLAB Online 中打开

The standard MATLAB approach:

J = [1,2,3,4,5,6,1,2,3,4,5,6];
P = sum(reshape(J,[],4),1)
P = 1×4
     6    15     6    15
H = J(1:4).*P
H = 1×4
     6    30    18    60

DoinK 2023-6-10

thank you sir, the code is so simple and exactly what i need.

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Answer 1

Alan Stevens 2023-6-10

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1981059-using-loop-to-sum-value-of-an-array-and-summation#answer_1253489

在 MATLAB Online 中打开

Here's one way:

J=[1 2 3 4 5 6 1 2 3 4 5 6];
step = 3;
ix = 1:step:numel(J);
for i = 1:numel(ix)
    p(i) = sum(J(ix(i):ix(i)+step-1));
end
disp(p)
     6    15     6    15