How to derive/integrate plotted data?

I have data points that I'm plotting from an excel sheet that I would like to create a derivate or integral plot of. I've been plotting them via duration because the data is time coded, but I think having the x-axis be time is preventing me from getting derivaties or integrals.

I've tried diff to create derivatives but all I get is a perfectly flat line at 0. it looks like dy is being stored as a sym?

I've tried cumtrapz to get an integral but all I get is the base graph.

How do i fix this and actually get the derivative plot of my graph? And would a similar process follow for create an integral?

%

clear

datasource = "xxxxxxxxxxx.xlsx"

%importing data

disp("Importing Flight Data...")

Sheet1 = readtable(datasource,'PreserveVariableNames',true);

disp("Done")

disp("Importing Division Data...")

Sheet2 = readtable(datasource, 'sheet', 2, 'ReadRowNames',false, 'VariableNamingRule','preserve');

disp("Done")

%}

format longG;

TimetoEnd=(height(Sheet1)-1)*0.032*1000;

numManuRows=height(Sheet2);

MaxVar=(width(Sheet1)-1);

%plot x axis with time

t=duration(12,00,00,000:032:TimetoEnd,"format","hh:mm:ss.SSS");

tdoub=milliseconds(t/86400000);

Prompt which variable

while true

prompt = "Which variable would you like to see? Type 0 to end. ";

i = input(prompt);

if or(i<=0,MaxVar<i)

disp ("-------------End-------------")

break

end

y = eval(sprintf('Sheet1.Variable%i',i));

clf

plot(t,y,'k'); %plot graph

hold on;

pause(3);

%what follows is me trying to plot the derivative

syms x;

dy=diff(y,tdoubint);

plot(t,dy,'b');

%naming graph

graphname="Variable %d Derivative";

str2=sprintf(graphname,i);

title (str2);

%

disp("Creating Divisions...")

for m=1:numRows

dividename=Sheet2.ID{m};

dividetime = hours(Sheet2.Time(m) * 24);

dividetime.Format = 'hh:mm:ss.SSS';

if isnan(Sheet2.Duration(m)) == 1;

xline(dividetime,'g',{dividename});

elseif mod(m,2) == 1

xline(dividetime,'r',{dividename});

else

xline(dividetime,'b',{dividename});

end

end

%}

disp("Done")

%end

[Torsten]

We don't have your data - so we cannot run your code.

I suggest plotting the inputs to "diff" and "cumtrapz" just before you call the functions for differentiation and integration.

There is no need to define symbolic variables to use these functions.

[Walter Roberson]

   y = eval(sprintf('Sheet1.Variable%i',i));

Instead of using eval, you can use

   y = Sheet1.("Variable" + i));