Finding local minima and maxima of DSC curves using islocalmin and islocalmax

DSC (Differential Scanning Calorimetry) is a thermal analysis method used in material science and chemistry to understand the thermal behavior of polymers or other organic/inorganic materials. The test is usually performed by a first heating cycle (to melt all the microcrystalline regions), followed by a cooling phase and a second heating. It is during the cooling and second heating that the crystallization and melting temperatures of a material are measured in the form of the temperature at which the heating has a local minimum or maximum.

The issue here: it is highly desirable to have a process for finding the crystallization and melting temperatures automatically, and I tried to use the islocalmin and islocalmax functions of matlab to find these values. As can be seen, multiple local minima and maxima are detected (symbols: red for minima and blue for maxima) but a lot of junk is also detected. In addition, there is an overlap in the minima and maxima, which means that, for some reason that I cannot understand, the program considers these both as minima and maxima. This is especially problematic in the section where a large naumber of points are detected nect to each other.

What I am interested in is only the local mainima/maxima pointed to by arrows. Is there a way to make the detection more specific to avoid the multiplicity seen here and reliably detect the most crucial points?

[Mathieu NOE]

hello

can you share the data and code ?

[Saeid]

Sure, but the DSC files are really large. I have added the example input files and the code in the attachment.

[Mathieu NOE]

so this is the figure I get with the two data files

what is the relationship betweent the figure in this post (above) and what I get ?

[Saeid]

My apologies. I just attached a slightly modified version which generates a graph similar to the graphics that I originally posted. You can select both files when asked, but it will still just load one file (for simplicity).

[Mathieu NOE]

hello again

I think I needed to modify your code to make sure the 1st file is selected ({'TestForMatlab_1.txt'})

otherwise the second appars first in the list gievn by

[FileName,FilePath,~] = uigetfile({'*.txt*'},'MultiSelect','On');

FileName = 1×2 cell array

{'TestForMatlab_2.txt'} {'TestForMatlab_1.txt'}

clc; clear all; format long g; close all
[FileName,FilePath,~] = uigetfile({'*.txt*'},'MultiSelect','On');
OutFile='AllOutput.xlsx';
% IF=length(FileName);

FilePath = pwd;
FileName = {'TestForMatlab_1.txt'};
IF=length(FileName);

for ii=1:IF
    InFile=char(FileName(ii)); 
    InFilePath=fullfile(FilePath,char(FileName(ii)));
    RAWW=readtable(InFilePath,'Delimiter','tab');
    RAWW=table2array(RAWW); RAWW=replace(RAWW,',','.');
    Data=str2double(RAWW);
    InDat=fileread(InFilePath);
    ISize=strfind(InDat,'Size');
    Img=strfind(InDat,'mg');
    SampleWeight=InDat(ISize(1)+4:Img(1)-1);
    mSample(ii)=str2double(replace(SampleWeight,',','.'));
    TT=Data(:,2);WW=Data(:,3)/mSample(ii); tt=Data(:,1);
    TW=[TT WW];
    IsMinW=islocalmin((WW),'FlatSelection', 'first'); 
    IsMaxW=islocalmax((WW),'FlatSelection', 'first'); 
    T_WMin=TT(IsMinW); WMin=WW(IsMinW); 
    T_WMax=TT(IsMaxW); WMax=WW(IsMaxW); 
    TabName=['43281_' num2str(ii)];
    HeatingRate=gradient(TT)./gradient(tt);
    %xlswrite(OutFile,TW,TabName);
    subplot(2,2,[1 3])
    plot(TT,WW,'k-',T_WMin,WMin,'ro',T_WMax,WMax,'b*','LineWidth',1.5)
    hold on;
    %zz=findchangepts(WW)
    subplot(2,2,2)
    %plot(tt,TT,'LineWidth',1.5)
    plot(linspace(1,length(TT),length(TT)),WW,'LineWidth',1.5)
    %
    %plot(tt,gradient(TT),'LineWidth',1.5)
    subplot(2,2,4)
    plot(linspace(1,length(TT),length(TT)),HeatingRate,'LineWidth',1.5)
    %plot(tt,gradient(TT))
    %plot(tt,TT,'LineWidth',1.5)
    hold on
    TMax=max(unique(floor(TT(islocalmax(TT)))))'
    TMin=min(unique(floor(TT(islocalmin(TT)))))'
    %size(abs(TT-TMin)>1)
end

[Saeid]

Hi Matthieu,

I am not sure if I understand correctly that you have now changed my code to get rid of the multiple minima/maxima or if this is just a question? If that's a question, then the answer is that you can of course only load one file or mutliple files. But if the attached code is supposed to be changed, I ran it, and it seems to give the same results.

[Mathieu NOE]

hello

suggestion for today - late evening

clc; clear all; format long g; close all
% [FileName,FilePath,~] = uigetfile({'*.txt*'},'MultiSelect','On');
OutFile='AllOutput.xlsx';
% IF=length(FileName);

FilePath = pwd;
FileName = {'TestForMatlab_1.txt'};
IF=length(FileName);

for ii=1:IF
    InFile=char(FileName(ii)); 
    InFilePath=fullfile(FilePath,char(FileName(ii)));
    RAWW=readtable(InFilePath,'Delimiter','tab');
    RAWW=table2array(RAWW); RAWW=replace(RAWW,',','.');
    Data=str2double(RAWW);
    InDat=fileread(InFilePath);
    ISize=strfind(InDat,'Size');
    Img=strfind(InDat,'mg');
    SampleWeight=InDat(ISize(1)+4:Img(1)-1);
    mSample(ii)=str2double(replace(SampleWeight,',','.'));
    TT=Data(:,2);WW=Data(:,3)/mSample(ii); tt=Data(:,1);
    
    % keep only positive slope (of TT) data
    ind= find(diff(TT)>100/1e4);
    TT=TT(ind);WW=WW(ind); tt=tt(ind);
    TW=[TT WW];
    % add some  smoothing to avoid "multi hits" of islocalmin
    WW = smoothdata(WW,'gaussian',20);
    
    IsMinW=islocalmin((WW),'FlatSelection', 'center'); 
    IsMaxW=islocalmax((WW),'FlatSelection', 'center'); 
    IsMinW = find(IsMinW);
    IsMinW = [IsMinW(1) IsMinW(end)]; % forget the intermediate points , keep only  first and last one
    IsMaxW = find(IsMaxW);
    IsMaxW = [IsMaxW(1) IsMaxW(end)]; % forget the intermediate points , keep only  first and last one
    
    T_WMin=TT(IsMinW); WMin=WW(IsMinW); 
    T_WMax=TT(IsMaxW); WMax=WW(IsMaxW); 
    TabName=['43281_' num2str(ii)];
    HeatingRate=gradient(TT)./gradient(tt);
    %xlswrite(OutFile,TW,TabName);
    subplot(2,2,[1 3])
    plot(TT,WW,'k-',T_WMin,WMin,'rd',T_WMax,WMax,'bd','LineWidth',1.5,'Markersize',15)
    hold on;
    %zz=findchangepts(WW)
    subplot(2,2,2)
    %plot(tt,TT,'LineWidth',1.5)
    plot(linspace(1,length(TT),length(TT)),WW,'LineWidth',1.5)
    %
    %plot(tt,gradient(TT),'LineWidth',1.5)
    subplot(2,2,4)
    plot(linspace(1,length(TT),length(TT)),HeatingRate,'LineWidth',1.5)
    %plot(tt,gradient(TT))
    %plot(tt,TT,'LineWidth',1.5)
    hold on
    TMax=max(unique(floor(TT(islocalmax(TT)))))'
    TMin=min(unique(floor(TT(islocalmin(TT)))))'
    %size(abs(TT-TMin)>1)
end