Add value to previous value while using a for loop

Question

Vance Blake 2020-8-29

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https://ww2.mathworks.cn/matlabcentral/answers/586034-add-value-to-previous-value-while-using-a-for-loop

评论： stozaki 2020-8-29

Hi I am trying to compute the summation of a series of two values and then dvide them using a for loop and calling a function. The values of i can range from 1 to N and I want to sum them according to this relationship COM(from 1 to N) = [m(1)*x(1)]/m(1)+[m(2)*x(2)]/m(2)+...+[m(N)+x(N)]/m(N) I have posted what I have so far but cant crack how to add the previously calculated value to the new one. Any help would be greatly appreciated!

% Part A
N = 1:1:100;
SizeofN = size(N,2);
for i = 1:SizeofN
    m(i) = i^(1.1);
    x(i) = i^(2);
    CoM_num(i) = m(i)*x(i);
    CoM_denom(i) = m(i);
end
for j = 1:SizeofN
    CoM_tot(j) = CoM_num(j)/CoM_denom(j); 
end

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Answer 1

stozaki 2020-8-29

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https://ww2.mathworks.cn/matlabcentral/answers/586034-add-value-to-previous-value-while-using-a-for-loop#answer_486620

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Hello Vance,

Try adding the following to your script. COMTOT is the cumulative sum.

COMTOTALL = cumsum(CoM_tot);
COMTOT = COMTOTALL(end);

function : cumsum

Regards,

stozaki

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Vance Blake 2020-8-29

编辑：Vance Blake 2020-8-29

在 MATLAB Online 中打开

Hi stozaki, so I would like to calculate the cumulative total of the columns in the row vector specified by the current iteration number. So If im on iteration 3 it would sum the first 3 columns in CoM_tot. I have upgraded my code from when I posted but I can't seem to get the fucntion and function call right to perform that operation. Here is what I have and this is the error i get

Output argument "CoM_totM" (and maybe others) not assigned during call to

M = 10:1:100;
LengthofM = length(M);
for n = M:LengthofM
    [CoM_totM] = CenterMassCalc(M(n));
end
function [CoM_totM] = CenterMassCalc(M)
SizeofM = size(M,2);
for k = 10:SizeofM
    m(k) = k^(1.1);
    x(k) = k^(2);
    CoM_num(k) = m(k)*x(k);
    CoM_denom(k) = m(k);
    CoM_totM(k) = sum(CoM_num(1:k))/sum(CoM_denom(1:k));
    
end
end

stozaki 2020-8-29

在 MATLAB Online 中打开

Hi Vance,

The cause of the error is that CoM_totM has not been initialized, so an error occurs if the result of the CenterMassCalc function is undefined.

M = 10:1:100;
LengthofM = length(M);
for n = M:LengthofM
    [CoM_totM] = CenterMassCalc(M(n));
end
function [CoM_totM] = CenterMassCalc(M)
% initialize
CoM_totM = [];
SizeofM = size(M,2);
for k = 10:SizeofM
    m(k) = k^(1.1);
    x(k) = k^(2);
    CoM_num(k) = m(k)*x(k);
    CoM_denom(k) = m(k);
    CoM_totM(k) = sum(CoM_num(1:k))/sum(CoM_denom(1:k));
    
end
end