Slope of a plotted function in a specified point.

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Edward Simpson Songel
Edward Simpson Songel on 12 Nov 2020
Answered: Star Strider on 15 Nov 2020
Hi,
I've currently plotted an array signal that displays x and F(x) (not in a continuous manner but in a discreet one as it's an array). The signal plot is shown below.
My question is if there is a way to find out the slope of a point in the plot or if you can somehow get a slope from two close points on the plot, so I can then calculate m (slope constant). I need this in order to find out the transfere function of the signal.
Thank you very much in advance.
Yours faithfully.
Edward.

Answers (2)

VBBV
VBBV on 13 Nov 2020
%if true
% code
%end
t = 1:100
y = sin(2*pi*t)
YY = gradient(y)
  1 Comment
Edward Simpson Songel
Edward Simpson Songel on 15 Nov 2020
Hello Vasishta,
What I meant is if there is any graphic instrument on the plot command or any command that I can use to measure the slope at each point. From your reply what I see you do is establish a time period t and then use a sine function to calculate the slope. But in my case, I've got a signal out from an output of a machine, and i need to study the slope of that empirical signal. Is there any way I can do that?
Thank you very much for your reply and attention.
Edward.

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Star Strider
Star Strider on 15 Nov 2020
It would be easier to have your data.
Try this:
xv = linspace(0, 5); % Create Data
yv = sin(2*pi*xv*2.5); % Create Data
slopefcn = @(xsel,xv,yv) interp1(xv, gradient(yv)./gradient(xv), xsel); % Interpolate Slope At ‘xsel’
yval = @(xsel,xv,yv) interp1(xv, yv, xsel); % Interpolate ‘yval’ At ‘xsel’
xsel = 2.35; % Selected ‘X’ Value
ysel = yval(xsel,xv,yv); % Corresponding ‘Y’ Value
m = slopefcn(xsel, xv, yv); % Calculate Slope
b = ysel - m*xsel; % Calculate Y-Intercept (To Draw Line)
calcLine = m*(xsel+[-1 1]*0.05) + b; % Calculate Line For Plot
figure
plot(xv, yv)
hold on
plot(xsel, ysel, '+r') % Plot Point (Demonstration Only)
plot(xsel+[-1 1]*0.05, calcLine, '-r') % Plot Line (Demonstration Only)
hold off
My code calculates the slope at ‘xsel’ and then plots a line using it in order to demonstrate that it works. That part of the code is not necessary if you do not want to plot a line at the ‘xsel’ point. The data do not need to be regularly-sampled for it to work.

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