Why would this happen???

When I copy and paste a date and time from one MS Excel file to another, the value was kept the same but after formatting it to the Time format, the date went almost 4 years back!!!

Simulink model of Continuous Stirred-Tank Reactor in series

Here's a simple Simulink model I created today. This model simulates the concentration in three Continuous Stirred-Tank Reactor (CSTR) in a row and how these concentration values affected by the influent concentration. Sometimes the CSTR is also called well-mixed continuous flow through reactor.

The S-function of this CSTR model is shown below.


function [sys, x0 str, ts]=cstr_sfcn(t,x,u,flag,Cinit)
switch flag
    case 0 %initialize
        str=[];
        ts=[0 0];
        x0=Cinit;
        
        s=simsizes;
        s.NumContStates=1;
        s.NumDiscStates=0;
        s.NumOutputs=1;
        s.NumInputs=1;
        s.DirFeedthrough=0;
        s.NumSampleTimes=1;
        
        sys=simsizes(s);
        
    case 1 % derivatives


        sys=cstr(t,x,u);
    
    case 3 %output
        sys=x;
        
    case {2 4 9}
        sys=[];
    otherwise
        error(['unhandled flag=', num2str(flag)])
end


And below is the function of the reactor.


function dx=cstr(t, x, u)
Ca=x;
dCa=0.2*(u-Ca);
dx=dCa;

The Simulink model looks like this:

All of the three tanks has the same characteristics, except the initial concentrations were different.
C1(0)=5, C2(0)=3, and C3(0)=1. And the influent concentration was simulated by the pulse generator. The simulation results is shown below.

Set marker edge width in Matlab figures

A couple of days ago, I plotted about twenty figures and was trying to set the markers with thicker edge. This would be very easy if it was in Excel: just change the 'Marker Line Style' in the 'Format data series' tab. However, it was kind difficult to do in Matlab. At least I didn't get a good solution from the google results on that day.

Today I happened to find the solution when I was playing with Matalb just for fun. The fact is that the 'Marker Edge Width' is actually defined by the 'LineWidth', even when the plot does not use a line to connect the markers..

t=[1:5];
plot(t,sin(t), 's', 'Markersize', 20,'LineWidth', 5)  

Concatenate text and convert to numbers in Excel

I have a long Excel file which keep the date, month, year, hour, minute, and second in separate columns (figure 1). I want to use only one column to present the time, so it would be easier to plot the time as x-axis. Here is the function I used in cell G2:

=VALUE(CONCATENATE(A2,"/",B2,"/",C2," ",D2,":",E2,":", F2))

The Value function convert the text into numbers.
The Concatenate function connects all the text and convert them into one string.

remove any rows that contains a specific number in Matlab

In this post, I am trying to solve the problem given in the comments of one of the old post.

Here's the problem, if I understand it correctly:

a =

     1     2     3     4     5

     2     3     4   -99     6

     3     4     5     6     7

     4   -99     6     7     8

     5     6     7     8     9

How to remove all the rows that contains the number -99, in this case, the row #2 and #4?

And here's the code I wrote to do this job:

[rows col]=size(a); %count the number of rows and columns of matrix a

j=0; %initialize a counter;

for i=1: rows

    if sum(a(i,:)~=-99)==col; %This determines if the row has -99 or not, if not, do nothing

    else     %shift all of the rest of the rows up one row

        for m=i: rows-1; 

        a(m,:)=a(m+1,:);

        end

        j=j+1; %count how many rows has -99, which equals how many times the rows has been shifted up 

    end

end

b=a((1:rows-j),:); %get rid of the last j rows


The result is:



b =


     1     2     3     4     5
     3     4     5     6     7
     5     6     7     8     9

I hope this can work for you, Winifred. Thanks for your comments!

calculate average of every 5 cells in Excel

I have some data sampled at a rate of 1 sample per minutes. However, to use them as input for the following calculation, I have to convert them to the 5 minutes average. Simply put, I want to let B1=average(A1:A5), B2=average(A6:A10), B3=average(A11:A15), ... til B10=average(A46:A50).

I tried VBA code in Excel but didn't make it work. Then I tried Matlab-the code works but it's troublesome to copy/paste all the data between Excel and Matlab back and forth. Finally I figured out a simple way to do this in Excel, by using the OFFSET, ROW, and INDIRECT functions.

The formula to put in cell B1 is:

=AVERAGE(OFFSET(INDIRECT("A"&ROW(A1)*5-4),0,0,5,1))


The Row(A1) returns the row number of the cell, which is '1' in this case. So the INDIRECT("A"&ROW(A1)) *5-4, 0,0,5,1) returns the cell A1 to A5. When dragged to cell B2, the INDIRECT("A"&ROW(A2)) *5-4, 0,0,5,1) returns the cell A6 to A10. So I can drag this formula all the way down to B10 to finish this task.

The file looks like this:

How to concatenate two datasets in Matlab?

I wanted to vertically combine two datasets, so I can keep a long file of all the test results. The join function does not work here anymore. Of course this is even not a problem in Excel. However, to make it work in Matlab, it did took me a while to figure it out.

c=cat(1, a, b)