Double checking a for loop

2021 3 13
1 个回答
更新时间：2021 3 15
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Can someone just double check my for loop. Specifically the bolded line. I wanted to calculate the integrated chlorophyll and then use it to find the relative amount by dividing temp by the intchl. Technically speaking, if I add up all my relative chlorophyll values for each column they should equal 1. However, they are coming out totalling a little over one so I think I messed up.
for i=1:length(databin)
temp=databin{i};
temp=temp(:,Varnum);
VARfield(1:length(temp),i)=temp;
intchl(i) = nansum(0.5.*(temp(1:end -1) + temp(2:end))); %MARKED
%integrated chlorophyll should just be one number for each cast
relchl = temp/intchl(i);
VARfieldrel(1:length(relchl),i)=relchl;
end

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回答（1 个）

Sergey Kasyanov
Sergey Kasyanov 2021-3-13

0 个投票

Hello,
sum(temp/intchl) -> sum(temp)/intchl means that you divide sum of all values by sum of mean values. Lets write it in detail:
sum(temp) = x1 + x2 + x3 + ... + x(n-1) + x(n)
intchl = (x1+x2)/2 + (x2 + x3)/2 + ... + (x(n-2) + x(n-1)/2 + (x(n-1) + xn)/2 = x1/2 + x2 + x3 + .... + x(n-1) + xn/2 = sum(temp) - (temp(1) + temp(end))/2
It means that intchl is lower than sum(temp).
I think you should to calculate intchl as sum(temp).

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Sergey Kasyanov
Sergey Kasyanov 2021-3-13
Do you need to integrate temp over the bincenters?
In that case you can use next code:
intchl(i) = nansum((temp(1:end-1) + temp(2:end))/2.*diff(bincenters'))
Jacqueline Chrabot
Jacqueline Chrabot 2021-3-13
actually I think I do. because the data is binned by the depth which is the bincenters. That might work!
Jacqueline Chrabot
Jacqueline Chrabot 2021-3-13
Sergey, my bincenters is 1 by 20 .. I still get the error, "matrix dimensions don't agree".
Jacqueline Chrabot
Jacqueline Chrabot 2021-3-13
VARfield=NaN(totalrow(1),length(databin));
Varnum=11; %chloro
for i=1:length(databin)
temp=databin{i};
temp=temp(:,Varnum);
VARfield(1:length(temp),i)=temp;
%intchl(i) = nansum((temp(1:end-1) + temp(2:end)))
intchl(i) = nansum((temp(1:end-1) + temp(2:end))/2.*diff(bincenters'));
%integrated chlorophyll should just be one number for each cast
relchl = temp/intchl(i);
VARfieldrel(1:length(relchl),i)=relchl;
end
Sergey I'm stuck here and bolded line still gives me the error 'Matrix dimensions don't agree'
Sergey Kasyanov
Sergey Kasyanov 2021-3-15
I cant understand why error still exist. Maybe you should to use diff(bincenters) instead of diff(bincenters')?
Jacqueline Chrabot
Jacqueline Chrabot 2021-3-15
databin= cell(length(datafi),1)
for i = 1:length(datafi);
%for i =1;
temp=datafi{i};
minval = 0;
maxval = max(temp.Var7);
step = 0.25; %increase to 25, was at 0.10
bins = minval:step:maxval;
bincenters = bins + step/2;
bincenters = bincenters(1:length(bincenters)-1);
DATAavg_input = ones(length(bincenters),size(temp,2)).*NaN;
for xx = 2:length(bins);
nn = find(temp.Var7 >= bins(xx-1) & temp.Var7 < bins(xx));
DATAavg_input(xx-1,3:end) = nanmean(table2array(temp(nn,3:end)),1);
end
DATAavg_input(:,1)= datenum(datetime(temp.Var1(1), 'InputFormat', 'MM/dd/yyyy', 'Format', 'MM-dd-yyyy hh:mm:ss.SSSS') + temp.Var2(1));
%make sure to convert it back for contour using datetime
databin{i}=DATAavg_input;
end
DataBin = DATAavg_input;
Sergey, for the time being do you know how to convert back the time from the bolded line?? I tried using xticks later on in my script and realized all the date and times were the same so xtick was saying 00:00 for everything??

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