how can i extract data of specific dates in a big excel file and save in a different excel file?

Hi,

Please i would like to extract data of some specific dates in the output file (data.xlsx) of the following function, and save in another excel file (data1.xlsx). Can someone please help?

y0=[0.02352;0.00048;0.0288;0.00432;0.216;0.1104;0.1104;2;2;2;55;50;0.5];
h=0.0006944444;
tSpan=0:h: 535;
  M=[ 1 0 0 0 0 0 0 0 0 0 0 0 0 
       0 1 0 0 0 0 0 0 0 0 0 0 0 
       0 0 1 0 0 0 0 0 0 0 0 0 0 
       0 0 0 1 0 0 0 0 0 0 0 0 0 
       0 0 0 0 1 0 0 0 0 0 0 0 0 
       0 0 0 0 0 1 0 0 0 0 0 0 0 
       0 0 0 0 0 0 1 0 0 0 0 0 0 
       0 0 0 0 0 0 0 1 0 0 0 0 0 
       0 0 0 0 0 0 0 0 1 0 0 0 0 
       0 0 0 0 0 0 0 0 0 1 0 0 0 
       0 0 0 0 0 0 0 0 0 0 1 0 0 
       0 0 0 0 0 0 0 0 0 0 0 1 0 
       0 0 0 0 0 0 0 0 0 0 0 0 1];

options = odeset('RelTol',eps^20,'AbsTol',1e-2, 'Mass', M);
[tSol, ySol]=ode23t(@(t, y) MBBRFun5(t,y), tSpan, y0, options);
xlswrite('F:\Matlab\data.xlsx',[tSol, ySol]);

I would like to extract data for t=4, 6, 7, 9.... etc in data.xlsx

Thanks in advance

[Bob Thompson]

Is there something wrong with your current method? If so, what is it? Also, it looks like you have t as one of the variables in your ode23 calculation, but it relates to tspan. Are you looking to get t =4, or t(4) = ...?

[KIPROTICH KOSGEY]

Hi Bob, i would like to get t(4), t(6) ... etc as the experimental data were collected on these dates but the interations were done at intervals of h for t=0 to t=535 days. As it is, the code is calculating ySol data for every step.

Thanks in advance

[Bob Thompson]

What does t actually represent other than different values of tspan. I know I spoke about t(4) earlier, but from what I understand of your code, t(4) doesn't actually exist because t is a temporary assignment from tspan. If you want the four value of t use tspan(4).

vals = [4 6 7 9 ...]; % Identify the indices you want
tspan(vals); % This is the values you want

[KIPROTICH KOSGEY]

Thank you Bob

Answer 1

[Mir Amid Hashemi]

It might be useful to use Tall Arrays. These arrays are not completely loaded into memory if they are really big.

I would recommend to go to https://uk.mathworks.com/help/matlab/import_export/tall-arrays.html

Amid.