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Add value to previous value while using a for loop

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Vance Blake
Vance Blake on 29 Aug 2020
Commented: stozaki on 29 Aug 2020
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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Answers (1)

stozaki
stozaki on 29 Aug 2020
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

  2 Comments

Vance Blake
Vance Blake on 29 Aug 2020
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
stozaki on 29 Aug 2020
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
Even if you initialize CoM_totM, the result will be empty.
Is the processing you want to perform appropriate?
stozaki

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